United States
Environmental Protection
Agency
EPA 402-F-09-002 I Revised August 2009 I www.epa.gov/iaq
RESIDENTIAL
CLEANERS
(Second Edition)
A SUMMARY OF
AVAILABLE INFORMATION
Indoor Air Quality (IAQ)
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U.S. Environmental Protection Agency
Office of Air and Radiation
Indoor Environments Division
1200 Pennsylvania Avenue, NW
Mail code: 6609J
Washington, DC 20460
www.epa.gov/iaq
This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved
for publication. Mention of trade names, products, or services does not convey, and should not be interpreted as
conveying official EPA approval, endorsement or recommendation.
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TABLE OF CONTENTS
Summary 2
Introduction 4
Indoor Air Pollutants 5
Three Strategies To Reduce Indoor Air Pollutants 6
Types of Air Cleaners 7
Removal of Particles 8
Types of Particle-Removal Air Filters 8
Defining Efficiency and Effectiveness 9
Air Filters - Available Guidance for Their Comparison 10
Air Filters -Available Evidence of Their Usefulness 12
Portable Air Cleaners - Available Guidance for Their Comparison 13
Portable Air Cleaners -Available Evidence of Their Usefulness 14
Removal of Gaseous Pollutants by Sorbents 15
Types of Sorbents Used for Gaseous Pollutant Removal 16
Applications of Sorbents for Gaseous Pollutant Removal 11
Removal of Radon and Its Progeny 17
Deactivation or Destruction of Pollutants 18
Ultraviolet Germicidal Irradiation Cleaners 18
Photocatalytic Oxidation Cleaners 20
Ozone Generators 21
Will Air Cleaning Health from Indoor Air Pollutants? 23
Additional Factors to Consider 25
Installation 25
Operations and Maintenance 25
Cost 25
Inability to Remove Some Odors 26
Possible Effects of Particle Charging 26
Soiling of Walls and Other Surfaces 26
Noise 26
Conclusion 27
Glossary 28
30
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RESIDENTIAL AIR CLEANERS
Indoor air pollution is among the top five
environmental health risks. Usually the best way
to address this risk is to control or eliminate
the sources of pollutants and ventilate a home
with clean outdoor air. But opportunities for
ventilation may be limited by weather conditions
or by contaminants in the outdoor air.
If the usual methods of addressing indoor air
pollution are insufficient, air-cleaning devices may
be useful. Air filters and other air-cleaning devices
are designed to remove pollutants from indoor air.
Some are installed in the ductwork of a home's
central heating, ventilating, and air-conditioning
(HVAC) system to clean the air in the entire
house. Portable room air cleaners can be used to
clean the air in a single room or in specific areas,
but they are not intended to filter the air in the
whole house. Air-cleaning devices are categorized
by the type of pollutants—particulate and
gaseous—that the device is designed to remove
or destroy.
Two types of air-cleaning devices can remove
particles from the air: mechanical air filters and
electronic air cleaners.
Mechanical air filters, such as high efficiency
particulate air (HEPA) filters, remove particles
by capturing them on filter materials. Most
mechanical air filters are good at capturing larger
airborne particles—such as dust, pollen, some
mold spores, and animal dander—and particles
that contain dust mite and cockroach allergens.
But because these particles settle rather quickly,
mechanical air filters are not very good at
completely removing them from indoor areas.
Electronic air cleaners, such as electrostatic
precipitators, use a process called electrostatic
attraction to trap particles. Ion generators, or
ionizers, disperse charged ions into the air. These
ions attach to airborne particles, giving them a
charge so they can attach to nearby surfaces such
as walls or furniture, or to one another, and settle
faster. However, some electronic air cleaners can
produce ozone, a lung irritant.
Another type of air-cleaning device is a gas-phase
filter designed to remove gases and odors by either
physical or chemical processes.
Gas-phase air filters remove gaseous pollutants
by using a material called a sorbent, such as
activated carbon, to adsorb pollutants. Because
these filters are targeted at one or a limited
number of gaseous pollutants, they will not
reduce concentrations of pollutants for which they
were not designed. None are expected to remove
all of the gaseous pollutants in the air of a typical
home. Gas-phase filters are much less common in
homes than are particle air filters. One reason may
be the filter can become overloaded quickly and
may need to be replaced often.
Three types of air cleaners on the market are
designed to deactivate or destroy indoor air
pollutants: ultraviolet germicidal irradiation
(UVGI) cleaners, photocatalytic oxidation (PCO)
cleaners, and ozone generators sold as air cleaners.
UVGI cleaners use ultraviolet radiation from UV
lamps that may destroy biological pollutants such
as viruses, bacteria, and molds that are airborne
or growing on HVAC surfaces (e.g., cooling
coils, drain pans, or ductwork). UVGI cleaners
should be used with, but not as a replacement for,
filtration systems. Typical UVGI cleaners used
in homes have limited effectiveness in killing
bacteria and molds. Effective destruction of some
viruses and most mold and bacterial spores usually
requires much higher UV exposures than a typical
home unit provides.
PCO cleaners use UV lamps along with a
substance, called a catalyst, that reacts with the
light. These cleaners are designed to destroy
gaseous pollutants by changing them into
harmless products, but they are not designed
to remove particulates. The usefulness of PCO
cleaners in homes is limited because currently
available catalysts are ineffective in destroying
gaseous pollutants in indoor air.
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A Summary of Available Information
Ozone generators use UV lamps or electrical
discharges to produce ozone that reacts with
chemical and biological pollutants and transforms
them into harmless substances. Ozone is a potent
lung irritant, which in concentrations that do not
exceed public health standards, has little potential
to remove indoor air contaminants. Thus ozone
generators are not always safe and effective in
controlling indoor air pollutants.
Portable air cleaners generally contain a fan
to circulate the air and use one or more of the
air-cleaning technologies discussed above. They
may be an option if a home is not equipped with
a furnace or a central air-conditioning system.
Many portable air cleaners have moderate to large
air delivery rates for small particles. However,
most of the portable air cleaners on the market do
not have high enough air delivery rates to remove
large particles such as pollen and particles that
contain dust mite and cockroach allergens from
typical-size rooms.
Several other factors should be considered when
making decisions about using air-cleaning devices.
^ Installation: In-duct air-cleaning devices have
certain installation requirements that must be
met, including sufficient access for inspection
during use, repairs, and maintenance.
l» Major costs: These costs include the initial
purchase price and the cost of maintenance
(such as cleaning or replacing filters and parts)
and operation (electricity).
^> Odors: Air-cleaning devices designed to
remove particles cannot control gases and
some odors. The odor and many of the
carcinogenic gas-phase pollutants from
tobacco smoke, for example, will remain.
^ Soiling of walls and other surfaces: Typical
ion generators are not designed to remove
from the air the charged particles that they
generate. These charged particles may settle
on, and soil, walls and other room surfaces.
l» Noise: Noise may be a problem with portable
air cleaners that contain fans. Portable air
cleaners that do not have fans tend to be
much less effective than units that have them.
The ability to remove some airborne pollutants,
including microorganisms, is not, in itself, an
indication of an air-cleaning device's ability
to reduce adverse health effects from indoor
pollutants. Although air-cleaning devices may
help reduce levels of smaller airborne particles
including those associated with allergens, they
may not reduce adverse health effects, especially in
sensitive populations such as children, people who
have asthma and allergies, and the elderly. For
example, the evidence is weak that air-cleaning
devices are effective in reducing asthma symptoms
associated with small airborne particles such as
those that contain cat and dust mite allergens.
There are no studies linking the use of gas-phase
filtration, UVGI systems, or PCO systems in
homes to reduced health symptoms in
sensitive populations.
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RESIDENTIAL AIR CLEANERS
The best way to address residential indoor air
pollution usually is to control or eliminate the
source of the pollutants and to ventilate the home
with clean outdoor air. But ventilation may be
limited by weather conditions or the levels of
contaminants in the outdoor air.
If the usual methods of dealing with indoor air
pollutants are insufficient, air-cleaning devices may
be useful. Air filters and other air-cleaning devices
are designed to remove pollutants from indoor
air. They can be installed in the ductwork of most
home heating, ventilating, and air-conditioning
(HVAC) systems to clean the air in the entire
house, or the same technology can be used in
portable air cleaners that clean the air in single
rooms or specific areas. Most air-cleaning devices
are designed to remove particles or gases, but some
destroy contaminants that pass through them.
This publication focuses on air cleaners for
residential use; it does not address air cleaners used
in large or commercial structures such as office
buildings, schools, large apartment buildings,
or public buildings. It should be particularly
useful to residential housing design professionals,
public health officials, and indoor air quality
professionals. In addition to providing general
information about the types of pollutants affected
by air cleaners, this document discusses:
^ The effectiveness of air cleaning compared to
other strategies, such as source control and
ventilation, for reducing indoor air pollutants.
^ The types of air-cleaning devices available.
^ Guidelines that can be used to compare air-
cleaning devices.
^ The effectiveness of air-cleaning devices in
removing indoor air pollutants.
^ General information on the health effects of
indoor air pollutants.
^ Additional factors to consider when deciding
whether to use an air-cleaning device.
Please Note: The U.S. Environmental Protection Agency (EPA) neither certifies nor recommends
particular brands of home air-cleaning devices. While some home air-cleaning devices may be useful in
some circumstances, EPA makes no broad endorsement of their use, nor specific endorsement of any
brand or model. This document describes the performance characteristics of several types of air cleaners
sold for in-home use.
Federal pesticide law requires manufacturers of ozone generators to list an EPA establishment number
on the product's packaging. This number merely identifies the facility that manufactured the product.
Its presence does not imply that EPA endorses the product, nor does it imply that EPA has found the
product to be safe or effective.
Some portable air cleaners sold in the consumer market are ENERGY STAR® qualified. Please note the
following disclaimer on their packaging: "This product earned the ENERGY STAR by meeting strict
energy efficiency guidelines set by EPA. EPA does not endorse any manufacturer claims of healthier
indoor air from the use of this product."
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A Summary of Available Information
There are two categories of indoor air pollutants
that can affect the quality of air in a home:
particulate matter and gaseous pollutants.
Paniculate matter (PM) is composed of
microscopic solids, liquid droplets, or a mixture
of solids and liquid droplets suspended in air. Also
known as particle pollution, PM is made up of a
number of components, including acids such as
nitric and sulfuric acids, organic chemicals, metals,
soil or dust particles, and biological contaminants.
Among the particles that can be found in a
home are:
^> Dust as solid PM or fumes and smoke, which
are mixtures of solid and liquid particles.
^> Biological contaminants, including viruses,
bacteria, pollen, molds, dust mite and
cockroach body parts and droppings, and
animal dander.
Particles come in a wide range of sizes. Small
particles can be fine or coarse. Of primary concern
from a health standpoint are fine particles that have
a diameter of 2.5 micrometers (um) or less. These
particles (described as "respirable") can be inhaled;
they penetrate deep into the lungs where they
may cause acute or chronic health effects. Coarse
particles, between 2.5 and 10 um in diameter,
usually do not penetrate as far into the lungs; they
tend to settle in the upper respiratory tract. Large
particles are greater than 10 um in diameter, or
roughly one-sixth the width of a human hair. They
can be trapped in the nose and throat and expelled
by coughing, sneezing, or swallowing.
Respirable particles are directly emitted into indoor
air from a variety of sources including tobacco
smoke, ozone reactions with emissions from indoor
sources of organic compounds, chimneys and
flues that are improperly installed or maintained,
unvented combustion appliances such as gas stoves
and kerosene or gas space heaters, woodstoves, and
fireplaces. This category of particles also includes
viruses and some bacteria.
Among the smaller biological particles found
in a home are some bacteria, mold fragments
and spores, a significant fraction of cat and dog
dander, and a small portion of dust mite body
parts and droppings. Larger particles include dust,
pollen, some mold fragments and spores, a smaller
fraction of cat and dog dander, a significant
fraction of dust mite body parts and cockroach
body parts and droppings, and skin flakes.
Gaseous pollutants include combustion gases
and organic chemicals that are not attached to
particles. Hundreds of gaseous pollutants have
been detected in indoor air.
Sources of indoor combustion gases such as
carbon monoxide and nitrogen dioxide include
combustion appliances, tobacco smoke, and
vehicles whose exhaust infiltrates from attached
garages or the outdoors.
Sources of airborne gaseous organic compounds
include tobacco smoke, building materials
and furnishings, and products such as paints,
adhesives, dyes, solvents, caulks, cleaners,
deodorizers, cleaning chemicals, waxes, hobby
and craft materials, and pesticides. Organic
compounds may also come from cooking food;
from human, plant, and animal metabolic
processes; and from outdoor sources. Some
electronic air cleaners and laser printers may
generate the lung irritant ozone by design or as a
by-product.
Radon is a colorless, odorless, radioactive gas
that can be found in indoor air. It comes from
uranium in natural sources such as rock, soil,
ground water, natural gas, and mineral building
materials. As uranium breaks down, it releases
radon, which in turn produces short-lived
radioactive particles called "progeny," some of
which attach to dust particles. Radon progeny
may deposit in the lungs and irradiate respiratory
tissues. Radon typically moves through the
ground and into a home through cracks and holes
in the foundation. Radon may also be present
in well water and can be released into the air
when that water is used for showering and other
household activities. In a small number of homes,
building materials also can give off radon.1
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RESIDENTIAL AIR CLEANERS
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Three basic strategies to reduce pollutant
concentrations in indoor air are source control,
ventilation, and air cleaning.
Source control eliminates individual sources of
pollutants or reduces their emission. It is usually
the most effective strategy for reducing pollutants.
There are many sources of pollutants in the home
that can be controlled or removed.2 For example,
solid wood or alternative materials can be used in
place of pressed wood products that are likely to
be significant sources of formaldehyde. Smokers
can smoke outdoors. Combustion appliances can
be adjusted to decrease their emissions.
Ventilation is also a strategy for decreasing indoor
air pollutant concentrations. It exchanges air
between the inside and outside of a building. The
introduction of outdoor air is important for good
air quality. In a process known as infiltration,
outdoor air flows into the house through
openings, joints, and cracks in walls, floors, and
ceilings, and around windows and doors. Natural
ventilation describes air movement through open
windows and doors. Most residential forced air-
heating systems and air-conditioning systems do
not bring outdoor air into the
house mechanically. Two primary
ventilation methods can be used
in most homes: general ventilation
and local ventilation.
> General ventilation of the
living space, by way of
infiltration, natural ventilation,
or mechanical ventilation,
brings outdoor air indoors,
circulates air throughout the
home, and exhausts polluted
air outdoors. Although limited by weather
conditions, this method removes or dilutes
indoor airborne pollutants, thereby reducing
the level of contaminants and improving indoor
air quality (IAQ). Special consideration should
be given to the outdoor air used for ventilation.
It should be of acceptable quality and should
not contain pollutants in quantities that would
be considered objectionable or harmful if
introduced indoors. The use of ventilation
to reduce indoor air pollutants should be
evaluated carefully where there may be outdoor
sources of pollutants.
Localized ventilation by means of exhaust fans
in bathrooms and kitchens, and in some cases
by open windows and doors, removes excess
moisture and strong, local pollutants and keeps
them from spreading to other areas. Using
exhaust fans increases the amount of outdoor
air that enters a house.
Advanced designs for new homes are starting to
add a mechanical feature that brings outdoor
air into the home through the HVAC system.
Some of these designs include energy efficient
heat recovery ventilators to mitigate the cost of
cooling and heating this air during the summer
and winter. 3> 4
The use of air
cleaners alone
cannot ensure
adequate air
quality.
Air cleaning may be useful when
used along with source control
and ventilation, but it is not a
substitute for either method. The
use of air cleaners alone cannot
ensure adequate air quality,
particularly where significant
sources are present and ventilation
is insufficient. While air cleaning
may help control the levels of
airborne particles including those
associated with allergens and,
in some cases, gaseous pollutants in a home, air
cleaning may not decrease adverse health effects
from indoor air pollutants.
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A Summary of Available Information
OF AIR
Various technologies can be used in air-cleaning
devices. Filtration and electrostatic attraction
are effective in removing airborne particles.
Adsorption or chemisorption captures some
gaseous and vaporous contaminants. Some air
cleaners use ultraviolet light (UV) technology.
Ultraviolet germicidal irradiation (UVGI) has
been used to kill some microorganisms growing
on surfaces. Photocatalytic oxidation (PCO),
another UV light technology under development,
has the potential to destroy gaseous contaminants.
Ozone-generating devices sold as air cleaners use
UV light or corona discharge and are meant to
control indoor air pollutants.
Table 1 provides a brief summary of air-cleaning
technologies and the pollutants they are designed
to control.
Some air-cleaning devices are designed to be
installed in the ductwork of HVAC systems or to
be used in portable, stand-alone units.
In-duct or whole-house air-cleaning devices
typically are installed in the return ducts of HVAC
systems, as shown in Figure 1. The typical furnace
air filter is a simple air cleaner that captures
particles in the airstream to protect fan motors,
heat exchangers, and ducts from soiling. Such
filters are not designed to improve indoor air
quality, but the HVAC system can be upgraded by
using more efficient air filters to trap additional
particles. Other air-cleaning devices such as
electrostatic precipitators, UV lamps, and gas-
phase filters use sorption and chemical reaction
and are sometimes used in the ductwork of home
HVAC systems.
The fans in residential HVAC systems may
operate intermittently or continuously.
Continuous operation improves air circulation
and air cleaning, but this operation mode also
increases electrical energy consumption and costs.5
Portable air cleaners are available as small
tabletop units and larger console units. They are
used to clean the air in a single room, but not
in an entire house. The units can be moved to
wherever continuous and localized air cleaning
is needed. Larger console units may be useful in
houses that are not equipped with forced air-
heating systems and air-conditioning systems.
Portable air cleaners generally have a fan to
circulate the air and a cleaning device such as a
mechanical air filter, electrostatic precipitator, ion
generator, or UV lamp. Some units marketed as
having the quietest operation may have no fan;
however, units that do not have a fan typically are
OF
Filtration
Air filters
Gas-phase
filters
Particles
Gases
Ineffective in removing larger particles because most
settle quickly from the air and never reach the filters.
Used much less frequently in homes than particle air
filters. The lifetime for removing pollutants may be short.
UVGI
Biologicals
Bacterial and mold spores tend to be resistant to UV
radiation and require more light, longer exposures to UV
light, or both to be killed.
Other
Air Cleaners
PCO
Gases
Application for homes is limited because currently
available catalysts are ineffective in destroying gaseous
pollutants in indoor air.
Ozone
generators
Particles, gases,
biologicals
Sold as air cleaners, they are not always safe and effective
in removing pollutants. By design they produce ozone, a
lung irritant.
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RESIDENTIAL AIR CLEANERS
AIR
Return Air Duct
Air Filter Housing
Air Filter
3a Rigid Frame (such as a
chipboard)
3b Filter Media Restrainer
3c Filter Media (installed inside
the frame)
4 Air-Handling Unit that contains
a recirculation fan, heating
element, and cooling coil. (The
unit may be in a basement,
closet, or attic.)
5 Supply Air Duct
much less effective than units that have one. Air
cleaners may also have a panel filter with bonded
fine particles of activated carbon, or an activated
carbon filter encased in a frame, to remove gases
and odors. Some portable air cleaners referred to
as hybrid air cleaners use a combination of two or
more of the devices discussed above.
In this publication, air cleaners are categorized by
the types of pollutants, particulate and gaseous,
that the devices are designed to remove or
destroy.6'7
of
Air filters are designed to remove particulate
pollutants from indoor air. Their performance
depends not only on the airflow rate through the
filter media and the filter efficiency, but also on
factors such as the:
> Particle size and mass.
> Amount of dust on the air filter.
>• Airflow rate, velocity, path, and resistance
through the filter media.
> Mixing of air leaving the filter with the air in
the room.
> Leakage rate of air that bypasses the air filter.
Types of Particle-Removal Air Filters
Two general types of particle removal air-cleaning
devices are available: mechanical air filters and
electronic air cleaners. They are classified by the
method employed to remove particles of various
sizes from the air.
Mechanical air filters installed in a central
HVAC system or in a portable air cleaner
capture particles on filter media. Particles either
become trapped in the fibers of the filter or stick
to the filter because of an electrostatic charge.
Mechanical air filters come in two major types:
flat and pleated.
Flat or panel filters generally consist of coarse
glass fibers, coated animal hair, vegetable fibers,
synthetic fibers (such as polyester or nylon),
synthetic foams, metallic wools, or expanded
metals and foils. The filter media may be treated
with a viscous substance, such as oil, that causes
particles to stick to the fibers. Flat filters also
may be made of three types of permanently
electrostatically charged material: resin wool,
a plastic film or fiber called "electret," or an
electrostatically sprayed polymer. Their static
charge attracts and captures particles. The fibers
of electret filters are somewhat larger than the
fibers of other flat filters, resulting in relatively low
pressure drop and greater efficiency in filtering
smaller particles. The efficiency of electret filters
decreases as the media become loaded with
particles.
Pleated or extended surface filters are generally more
efficient than flat filters in capturing respirable
particles. Pleating the filter medium increases
surface area, reduces air velocity, and allows the
use of smaller fibers and increased packing density
of the filter without a large drop in airflow rate.
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A Summary of Available Information
A wire frame in the form of a pocket or V-shaped
cardboard separators may be used to maintain the
pleat spacing. The media used in pleated filters are
fiber mats, bonded glass fibers, synthetic fibers,
cellulose fibers, wool felt, and other cotton-
polyester material blends.
High efficiency particulate air (HEPA) filters are
a type of extended surface filter. HEPA filters
usually are made of submicron glass fibers and
have a texture similar to blotter paper. They also
have a larger surface area and remove respirable
particles more efficiently than pleated filters.
Electronic air cleaners use a process called
electrostatic attraction to trap charged particles.
There are two types of electronic air cleaners:
electrostatic precipitators and ion generators.
Electrostatic precipitators have an ionization
section and a collecting plate section, both of
which use an external power source. The air
cleaner draws air through the ionization section,
where particles obtain an electrical charge. The
charged particles accumulate on a series of flat
plates called a collector that is oppositely charged.
Cleaning the collector plates is essential to
maintaining adequate performance.
Ion generators, or ionizers, disperse charged ions
into the air, similar to an electrostatic precipitator,
but ionizers do not have collecting plates. They
produce ions by means of corona discharge or
UV light. The ions attach to particles and give
them a charge so they adhere to nearby surfaces
such as walls, furniture, and draperies, or combine
with other particles and settle on room surfaces.
Ion generators are the simplest form of electronic
air cleaner and come in tabletop, portable, and
ceiling mounted units.
Like mechanical filters, electronic air cleaners
can be installed in HVAC systems or used in
portable units. Although electronic air cleaners
remove small particles, they do not remove gases
or odors. And because electronic air cleaners
use high voltage to generate ionized fields, they
can produce ozone, either as a by-product or by
design.8 Residential indoor ozone concentrations
may be affected by the amount of ozone emitted
by electronic air cleaners, which varies among
models. Even at concentrations below public
health standards, ozone reacts with chemicals
emitted by such common indoor sources as
household cleaning products, air fresheners,
deodorizers, certain paints, polishes, wood
flooring, carpets, and linoleum. The chemical
reactions produce harmful by-products that may
be associated with adverse health effects in some
sensitive populations. The ozone reaction by-
products that may result include ultrafine particles
(smaller than 0.1 um in diameter), formaldehyde,
ketones, and organic acids.8'9'10 Concerns about
ozone and ozone-generating devices are discussed
in the EPA document Ozone Generators that are
Sold as Air Cleaners, posted on the EPA Web site
at www.ega.gov/iaq/piibs/ozonegeri.htrnl.
Defining Efficiency and Effectiveness
To choose air-cleaning devices and use them
properly, it is important to understand the
difference between efficiency and effectiveness.
The efficiency of an air-cleaning device, usually
expressed as a percentage, is a measure of its
ability to remove airborne particles or gaseous
pollutants from the air that passes through it. The
effectiveness of an air-cleaning device is a measure
of its ability to reduce airborne particle or gaseous
pollutant concentrations in an occupied space.
The efficiency of air filters used in ducts of
HVAC systems or in portable air cleaners varies
based on the airflow rate and the particulate
matter load. The effectiveness of an air-cleaning
device in removing pollutants from an occupied
space depends on three factors: its efficiency,
the amount of air being filtered, and the path
that the clean air follows after it leaves the filter.
For example, a filter may remove 99 percent of
the particles from the air that passes through
it (i.e., have 99 percent efficiency). However,
if the airflow rate through the filter is only 10
cubic feet per minute (cfm) in a typical room of
approximately 1,000 cubic feet (e.g., 10' x 12'
x 8'), the filter will be relatively ineffective at
removing particles from the air (i.e., 10 times less
effective than if the airflow rate were 100 cfm).
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RESIDENTIAL AIR CLEANERS
Higher efficiency filters remove larger and smaller
airborne particles more efficiently. Homeowners
should take care to properly install them in
HVAC systems and make sure that leakage of air
bypassing the filter is minimized. The higher a
filter's efficiency, the more attention must be paid
to its sealed installation because increased airflow
resistance is more likely to create leaks. Air filter
effectiveness may be substantially reduced if air
leaks through a poorly installed filter frame and
its holding system.11'12 Leakage of air bypassing a
HEPA filter used in a portable, stand-alone unit
may also reduce the filter's expected efficiency.
Effectiveness may be decreased if air exiting an
exhaust grille of the HVAC system is not well
mixed with room air before re-entering the
system. This situation can occur if air return and
intake vents are too close together.
Air Filters - Available Guidance for Their
Comparison
Several standardized methods have been
developed to measure the efficiency of different
types of air filters installed in the ductwork of
HVAC systems. They can be used to compare
the performance of air filters made by different
companies. The American Society of Heating,
Refrigerating and Air-Conditioning Engineers
(ASHRAE) and the Institute of Environmental
Sciences and Technology (IEST) have published
voluntary standards for rating air filters. The
IEST is now the recognized standard-setting
organization for the former Military Standard 282
developed by the U.S Department of Defense for
rating HEPA filters. The standards do not rate the
air filters' effectiveness; rather, they compare the
performance of various filters.
Particle removal efficiency can be assessed by
four standard methods: the weight arrestance
test, atmospheric dust spot efficiency test, dioctyl
phthalate (DOP) penetration test, and particle
size removal efficiency (PSE) test.
The weight arrestance test,13 defined in
ASHRAE Standard 52.1-1992, * is generally
used to evaluate low efficiency filters designed
to remove the largest and heaviest particles.
These filters are commonly used in residential
furnaces and air-conditioning systems to protect
system components, or as upstream filters to
protect higher efficiency filters. In this test, a
synthetic dust is fed into the air cleaner and the
percentage by weight of the dust the filter traps,
called "arrestance," is determined. The weight
arrestance test may be of limited value in assessing
the removal of smaller, respirable particles because
particles in the test dust are generally larger than
those that can be inhaled deeply into the lungs.
The atmospheric dust spot efficiency test,13
also defined in ASHRAE Standard 52.1-1992,*
is generally used to rate medium-efficiency filters
in removing fine airborne dust particles that can
soil walls and other interior surfaces. A naturally
occurring atmospheric dust is fed into the air
cleaner to test its ability to reduce soiling of a
clean paper target as an indication of the cleaner's
capability to remove fine particles from the air.
The DOP penetration test,14 described in the
IEST-RP CC001.4 test method, is used to rate
true HEPA filters. A DOP cloud of uniform
0.3 um particles is fed into the filter. The
concentration of penetrating smoke measured
upstream and downstream of the filter determines
the filter efficiency, or the percentage of particles
the filter removes.
The PSE test,15 described in ASHRAE Standard
52.2-2007, provides a composite minimum
efficiency for removing particles of specific size
by filters incrementally loaded with synthetic
dust. The PSE test method does not eliminate the
need for DOP penetration and arrestance testing.
Very low-efficiency air filters, such as furnace
filters, must also be tested in accordance with
the weight arrestance method. The composite
minimum efficiency values are averaged and used
to determine the air cleaner's minimum efficiency
reporting value (MERV). The MERV ranges
from a low of 1 to a high of 20. The PSE test
*ASHRAE Standard 52.1.1992, Gravimetric and Dust-Spot Procedures for Method of Testing Air-Cleaning Devices Used in GeneralVentilationfor
Removing Particular Matter was withdrawn in spring 2009. Information previously found in this standard is now included via Addendum B to
ANSI/ASHRAE Standard 52.2, Method of Testing General VentilationAir-CleaningDevices for Removal Efficiency by Particle Size. The addendum
mandates calculation of weight arrestance for filters with Minimum Efficiency Reporting Values (MERVs) of 1 to 4 and atmospheric dust spot
efficiency for filters with MERVs of 5 to 16.
-------
A Summary of Available Information
2:
N PP 1 111 1
i
MERV
20
19
18
17
16
15
14
13
12
1 1
10
9
8
7
6**
5
4
3
2
1
Particle Size Removal
Efficiency, Percent in Particle
Size Range, fJm
0.3 to 1
1 to 3
3 to 10
> 99 999 ^ O.I- 0.2 ^m
particle size
> 99.999 ~>
I in 0.3 /urn
> 99.99 > particle size
> 99.97 J
> 95
85-95
75-85
< 75
—
—
—
—
—
:
> 95
> 90
> 90
> 90
> 80
65-80
50-65
< 50
—
:
> 95
> 90
> 90
> 90
> 90
> 85
> 85
> 85
> 70
50-70
35-50
20-35
< 20
< 20
< 20
< 20
Dust-Spot
Efficiency
Percent
—
—
> 95
90-95
80-90
70-75
60-65
50-55
40-45
30-35
25-30
< 20
< 20
< 20
< 20
< 20
< 20
Particle Size and
Typical Controlled
Contaminant
< 0.3 fJm
Virus (unattached)
Carbon dust
Sea salt
All combustion smoke
0.3-1 JJm
All bacteria
Droplet nuclei (sneeze)
Cooking oil
Most smoke
Insecticide dust
Most face powder
Most paint pigments
1-3 fJm
Legionella
Humidifier dust
Lead dust
Milled flour
Auto emission particles
Nebulizer drops
3-1 Opm
Mold
Spores
Dust mite body parts and
droppings
Cat and dog dander
Hair spray
Fabric protector
Dusting aids
Pudding mix
Powdered milk
> lOjJm
Pollen
Dust mites
Cockroach body parts and
droppings
Spanish moss
Sanding dust
Spray paint dust
Textile fibers
Carpet fibers
Typical Applications
Electronics manufacturing
Pharmaceutical
manufacturing
Carcinogenic materials
Superior commercial
buildings
Hospital inpatient care
General surgery
Superior residential
Better commercial
buildings
Hospital laboratories
Better residential
Commercial buildings
Industrial workplaces
Minimum filtration
Residential window air
conditioners
Typical Air Filter/Cleaner
Type
HEPA/ULPA Filters*
Bag Filters - Nonsupported
(flexible) microfine fiberglass or
synthetic media, 12 to 36 inches
deep.
Box Filters - Rigid style
cartridge,
6 to 12 inches deep.
Pleated filters -Extended
surface with cotton or polyester
media or both, 1 to 6 inches
thick.
Box Filters - Rigid style
cartridge,
6 to 12 inches deep.
Pleated filters -Extended
surface with cotton or polyester
media or both, 1 to 6 inches
thick.
Cartridge filters -Viscous cube
or pocket filters
Throwaway -Synthetic media
panel filters
Throwaway - Fiberglass or
synthetic media panel, 1 inch
thick.
Washable- Aluminum mesh,
foam rubber panel
Electrostatic - Self-charging
(passive) woven polycarbonate
panel
This table is adapted from ANSI/ASHRAE Standard 52.2-2007. <5
*The last four MERV values of 17 to 20 are not part of the official standard test, but have been added by ASHRAE for comparison purposes. Ultra Low
Penetration Air filters (ULPA) have a minimum efficiency of 99.999 percent in removing 0.3 \lm particles, based on the IEST test method. MERVs between 17
and 19 are rated for O.SjJm particles, whereas a MERV of 20 is rated for 0.1 to 0.2 \lm particles.
** For residential applications, the ANSI/ASHRAE Standard 62.2-2007" requires a filter with a designated minimum efficiency of MERV 6 or better.
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RESIDENTIAL AIR CLEANERS
may not be appropriate for evaluating electronic
air cleaners because the dust used contains
conductive carbon, which may cause electrical
shorting and thus compromise the effectiveness of
these devices and alter their MERV. The dust-
loading procedure may also affect the efficiency of
electrostatically charged filters.
A cross-reference of atmospheric dust spot
efficiency tests to the MERV is shown in Table 2.
This table shows the minimum PSE in three size
ranges for each MERV. A consumer can use the
table to identify the MERV required to control a
specific pollutant. While these standards cannot
by themselves predict the actual effectiveness of
any filter over its lifetime, they can generally be
used to compare the performance characteristics
of one air filter with another.
Air Filters - Available Evidence of Their
Usefulness
Whether installed in the ducts of HVAC systems
or used in portable air cleaners,
most air filters have a good
efficiency rating for removing
larger particles when they remain
airborne. These particles include
dust, pollen, some molds, animal
dander, and those that contain
dust mite and cockroach body
parts and droppings. But because
these particles settle rather
rapidly from the air, air filters are
somewhat ineffective in removing
them from indoor areas. And
although human activities such
as walking and vacuuming, or the high velocity
air exiting supply vents, can re-suspend particles,
most of the larger particles will resettle before they
enter the HVAC system or portable air cleaner
and are removed by a particle air filter.
The appropriate type of particle removal air filter
can be chosen by looking at its MERV rating in
removing airborne particles from the airstream
that passes through it. MERV ratings can also
be used to compare air filters made by different
manufacturers.
Large particles
settle from the air
rapidly; therefore, air
filters are somewhat
ineffective in their
removal.
Flat or panel air filters with a MERV of 1 to 4
have low efficiency on smaller airborne particles,
but reasonable efficiency on large particles when
they remain airborne. These filters have low
airflow resistance and are relatively inexpensive.
Typically Vi to 1 inch thick, they are commonly
used in residential furnaces and air-conditioning
systems, and they are often used as pre-filters for
higher efficiency filters. For the most part, such
filters are used to protect the HVAC equipment
from the buildup of unwanted materials on fan
motors, heat exchangers, and other surfaces.
Pleated or extended surface filters with a MERV
of 5 to 13 have higher efficiency ratings than
panel filters. These medium-efficiency filters are
reasonably efficient at removing small-to-large
airborne particles. The airflow resistance of these
filters does not necessarily increase as the MERV
increases. Higher efficiency filters with a MERV
of 14 to 16 have a higher average resistance to
airflow than medium-efficiency filters. Higher
efficiency pleated filters, sometimes inaccurately
called "high efficiency," "HEPA,"
or "HEPA-type" filters, are
similar in appearance to true
HEPA filters, which have MERV
values of 17 to 20, but use less
efficient filter media.
The depth of these pleated or
extended surface filters may vary
from approximately 1 to 6 inches
for medium-efficiency models
and 6 to 12 inches for higher
efficiency filters. As the depth
and pleating increases, so does the area of the
filtration medium, helping to offset the increase
in resistance to airflow across the filter. Because
of their increased surface area, these filters often
have an extended life. The operating resistance of
a fully dust-loaded filter must be considered in
the design, because it is the maximum resistance
against which the fan operates. Generally, dust
loading results in increased filtration efficiency
along with an increase in pressure drop. Pressure
drop in media-type filters is greater than that in
electronic-type cleaners and slowly increases over
the filters' useful life.
-------
A Summary of Available Information
Some residential HVAC systems may not have
enough fan or motor capacity to accommodate
higher efficiency filters. Therefore, the HVAC
manufacturer's information should be checked
prior to upgrading filters to determine whether it
is feasible to use more efficient filters.
True HEPA filters with a MERV between 17
and 19 are defined by the IEST test method as
having a minimum efficiency between 99-97
percent and 99-999 percent in removing 0.3 um
particles. A MERV of 20 is rated for 0.1 to 0.2
um particles. HEPA filters have higher efficiencies
for removing both larger and smaller airborne
particles. True HEPA filters normally are not
installed in residential HVAC systems; installing
a HEPA filter in an existing HVAC system would
probably require professional modification of the
system. A typical residential air-handling unit
and the associated ductwork would not be able to
accommodate such filters because of their size and
increased airflow resistance. Specially built high
performance homes may occasionally be equipped
with true HEPA filters installed in a properly
designed HVAC system.
Manufacturers market HEPA filters to allergy
and asthma patients. Experimental data and
theoretical predictions indicate that medium-
efficiency air filters, MERV between 7 and 13,
are likely to be almost as effective
as true HEPA filters in reducing
the concentrations of most
indoor particles linked to health
effects.17 Available data indicate
that even for very small particles,
HEPA filters are not necessarily
the preferred option. For these
small particles, relatively large
decreases in indoor concentrations
(around 80 percent) are
attainable with medium filter
efficiency (such as a MERV of
13). Increasing filter efficiency
above a MERV of 13 results in only modest
predicted decreases in indoor concentrations of
these particles.* Predicted reductions in indoor
concentrations of cat and dust mite allergens
Filters that have a
MERV between 7
and 13 are likely
to be nearly as
effective as true
HEPA filters.
carried on small particles vary from 20 percent
with a MERV 7 filter to 60 percent using a
HEPA filter. Increasing filter efficiency above
a MERV of 11 does not significantly reduce
predicted indoor concentrations of animal dander.
Medium-efficiency air filters are generally less
expensive than HEPA filters and allow quieter
HVAC fan operation and higher airflow rates
than HEPA filters because they have less airflow
resistance. Pleated filters 1 to 2 inches thick
that have a MERV of 12 are available for use
in homes and may often be installed without
modifying residential HVAC systems; however,
manufacturer's information should be checked
prior to installation.
Electrostatic precipitators remove and collect
small airborne particles and have an initial
ASHRAE dust spot efficiency of up to 98 percent
at low airflow velocity. This efficiency will be
highest for clean electronic air cleaners. Electronic
air cleaners exhibit high initial efficiencies in
cleaning air, largely because of their ability to
remove fine particles. Their efficiency decreases as
the collecting plates become loaded with particles,
or as airflow velocity increases or becomes less
uniform.
Portable Air Cleaners - Available Guidance for
Their Comparison
The effectiveness of a portable
air cleaner depends on the air-
cleaning device's efficiency in
removing airborne pollutants, the
quantity of air being filtered, the
particle size, the size of the room
the air cleaner serves, and its
location in the space. A voluntary
standard is available for measuring
the effectiveness of portable air
cleaners in reducing airborne
pollutants in a room. It was
developed by the Association of
Home Appliance Manufacturers
(AHAM), a private voluntary standard-setting
trade association, and is recognized by the
American National Standards Institute.18 The
standard compares the effectiveness of portable
*Some air filters may be effective at reducing tobacco smoke particles, but they will not remove gaseous pollutants from tobacco smoke. While some gas-
phase filters may remove specific gaseous pollutants from the complex mixture of chemical compounds in tobacco smoke, none is expected to remove all
unwanted gaseous combustion pioducts Odoious and toxic oiganic gases may also e\apoiate from liquid tobacco smoke particles napped bv the all faltei'
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RESIDENTIAL AIR CLEANERS
air cleaners in a room size test chamber, measured
by the clean air delivery rate (CADR) for each of
three types of particles in indoor air: dust, tobacco
smoke, and pollen. Although AHAM uses tobacco
smoke particles to represent smaller airborne
particles, air cleaning should not be construed as
an effective way to address environmental tobacco
smoke. There are thousands of particulate and
gaseous chemical compounds, including many
known carcinogens, in tobacco smoke that cannot
be removed effectively by air cleaning.
Although AHAM uses the CADR concept to
evaluate the performance of portable air cleaners
in reducing particulate matter concentrations, the
CADR can be applied equally to the removal of
gaseous pollutants. The CADR does not apply
to whole-house air-cleaning devices installed in
HVAC ductwork.
The CADR is a measure of a portable air cleaner's
delivery of contaminant-free air, expressed
in cubic feet per minute. For example, an
air cleaner that has a CADR of 250 for dust
particles can reduce dust particle levels to the
same concentration as would be achieved by
adding 250 cfm of clean air.
The portable air cleaner's
removal rate competes with
other removal processes
occurring in the space,
including deposition of
particles on surfaces, sorption
of gases, indoor air chemical
reactions, and outdoor air
exchange. While a portable
air cleaner may not achieve
its rated CADR under all
circumstances, the CADR
value does allow comparisons
among portable air cleaners.
AHAM has a portable air-
cleaner certification program
and lists all certified cleaners
and their CADRs on its Web site at
www.cadr.org.19 AHAM's online directory of
certified portable air cleaners allows searches by
certified CADR ratings, suggested room size,
manufacturer, or brand name. The CADR
Most portable air
cleaners don't
effectively remove
large particles such
as dust, pollen,
some mold spores,
and particles
containing dust
mite and cockroach
allergens in rooms
of typical size.
values reported for selected portable air cleaners
are based on an 80-percent reduction in steady
particle concentrations. AHAM's recommended
effectiveness of 80 percent produces meaningful
reductions in contaminant concentrations
indoors. This level of effectiveness corresponds to
an air cleaner's capability to provide an amount
of clean air that is four to five times the volume of
the specified size room.9
Indoor particle concentrations are not always
constant over time. Some indoor pollutants might
be produced periodically from sources such as
hobby and craft materials or cooking food. These
intermittent pollutant sources have only a modest
effect on particle concentrations indoors compared
to sources of steady pollutant concentrations.
Some portable air cleaners sold to consumers
are ENERGY STAR® qualified. Earning the
ENERGY STAR means a product meets strict
energy efficiency guidelines set by EPA and the
U.S. Department of Energy. The ENERGY STAR
disclaimer label, which includes the following
statement, is placed on the product packaging
of ENERGY STAR qualified air cleaners: "This
product earned the ENERGY STAR
by meeting strict energy efficiency
guidelines set by the US EPA. US EPA
does not endorse any manufacturer
claims of healthier indoor air from the
use of this product."
Portable Air Cleaners - Available
Evidence of Their Usefulness
Many of the portable air cleaners
AHAM tested have moderate-to-large
CADR ratings for small particles
when used in rooms of appropriate
size.9 However, for typical room sizes,
most portable air cleaners currently on
the market do not have high enough
CADR values to remove effectively
large particles such as dust, pollen,
some mold spores, animal dander,
and particles containing dust mite and cockroach
allergens. Some portable air cleaners that use
electronic air cleaners may produce ozone, which
is a lung irritant.
-------
A Summary of Available Information
Studies have assessed portable air cleaners'
performance in removing airborne particles
as well as their limited clinical effects. Some
tests addressed the removal of tobacco smoke
particles.20'21'22 Limited testing on larger airborne
particles including those that contain cat, dog, and
dust mite allergens have also been performed.23'24'
25,26,27,28 ]y[anv experimental studies used portable
air cleaners equipped with HEPA filters, but the
available sources indicate that HEPA filters may
not be preferable to medium-efficiency filters
because of HEPA filters' lower air delivery due to
air bypassing the filter and to higher resistance to
airflow. In addition, portable air cleaners are not
effective at removing large particles because large
particles settle out of indoor air at a substantial
rate.
The effectiveness of portable air cleaners in
removing particles from indoor air depends on
the size of the particles. One paper9 reported that
air-cleaning effectiveness of at least 80 percent
can be achieved by portable air cleaners that
have moderate-to-high CADR ratings in homes
where small particles are the main concern. On
the other hand, for larger airborne particles, the
combination of small room size and high CADR
ratings may yield particle removal effectiveness of
80 percent or more. However, for typical rooms
larger than 200 square feet, most portable air
cleaners on the market do not have high enough
CADR values to remove large particles effectively.
This fact may account for the finding that portable
air cleaners are most likely to be effective in
reducing indoor concentrations of smaller airborne
particles such as those associated with cat or dust
mite allergens.26 However, air cleaning was not
found to be consistently and highly effective in
reducing respiratory symptoms since much of the
airborne allergens appear to be carried on
larger particles.26
Some manufacturers consider their hybrid
portable air cleaners, which use multiple air-
cleaning devices, to be more effective than
portable air cleaners that use a single device.
However, the effectiveness of these hybrid units
may suffer because more air cleaners arranged in
a series may mean increased air resistance, which
could decrease air delivery or cause air to bypass
the cleaner. Effectiveness may also be decreased
if air exiting the portable air cleaner outlet is not
adequately mixed with room air before re-entering
the unit.
Useful information about portable air cleaners
is available from Consumer Reports magazine.
Published by Consumers Union, an independent,
nonprofit organization, Consumer Reports provides
an annual review of products, their updated
reports, and ratings. The test method used by
Consumers Union is not intended to be the basis
for a standard for evaluating the performance
of air-cleaning devices; rather, Consumers
Union tests air cleaners using its own testing
procedures, rates the cleaners based on a variety
of criteria, and ranks them in charts that are easy
to understand. According to Consumers Union,
some portable air cleaners that use electrostatic
precipitators may produce measurable amounts of
ozone as a by-product.29 Electrostatic precipitators
may also make a crackling sound as they
accumulate dirt.
The placement of any portable air cleaner may
affect its performance. If there is a specific,
identifiable source of pollutants, the unit should
be placed so its intake is near that source. If there
is no specific source, the air cleaner should be
placed where it will force clean air into occupied
areas. It should not be situated where walls,
furniture, and other obstructions will block the
intake and outlet. A portable air cleaner will
be much more effective when all the doors and
windows in a room are closed. If the door to a
room where a portable air cleaner is located is
open, or if the HVAC system is operating, the
room air often will mix with air from throughout
the house, and the air cleaner will not reduce the
particle concentrations in the room as intended.
of
bj
Many different gas-phase air-filtration devices
are available; however, comparing and rating
the effectiveness of installed sorbent filters is
difficult because there is no standard test method.
II
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RESIDENTIAL AIR CLEANERS
ASHRAE Standard Project Committee 145 is
developing a standard method for evaluating
the effectiveness of gas-phase filtration devices
installed in the ductwork of residential HVAC
systems, but not in portable air cleaners.30
Gas-phase air filters remove gases and odors
by either physical or chemical processes. These
filters typically are designed to remove one or
more of the gaseous pollutants present at low
concentrations in the airstream that passes
through them. They are not, however, designed to
eliminate all gaseous pollutants. Air cleaners that
do not contain sorbent materials or photocatalytic
oxidation technology, discussed on page 20, will
not remove gaseous pollutants.
A sorbent filter's behavior depends on many
factors that can affect the removal of gaseous
contaminants:
> Airflow rate and velocity through the sorbent.
> Concentration of contaminants.
> Presence of other gaseous contaminants.
> Total available surface area of the sorbent.
(Some manufacturing techniques can
significantly reduce a filter's total surface area.)
> Physical and chemical characteristics of the
pollutants and the sorbent (such as weight,
polarity, pore size, shape, volume, and the type
and amount of chemical impregnation).
>• Pressure drop.
>• Removal efficiency and
removal capacity.
> Temperature and relative
humidity of the gas stream.
Gas-phase filters are much
less common than particle
air-cleaning devices in homes
because a properly designed
and built gas-phase filtration
system is too big for a typical residential HVAC
system or portable air cleaner. Other factors
that may contribute to the less frequent use of
gas-phase filters in home HVAC systems are
the filters' limited useful life, the fact that the
sorbent material must be targeted to specific
The limited lifetime of
gas-phase filters may
contribute to their
less frequent use in
home HVAC systems.
contaminants, the purchase price of the filters,
and the costs of adapting them to residential
applications, when possible, and of operating
them once they have been installed.
Types of Sorbents Used for Gaseous
Pollutant Removal
There are two main processes that remove
gaseous contaminants: a physical process known
as adsorption and a chemical reaction called
chemisorption.
Adsorption results from the physical attraction of
gas or vapor molecules to a surface. All adsorbents
have limited capacities and thus require frequent
maintenance. An adsorbent will generally adsorb
molecules for which it has the greatest affinity
and will allow other molecules to remain in the
airstream. Adsorption occurs more readily at lower
temperatures and humidity. Solid sorbents such
as activated carbon, silica gel, activated alumina,
zeolites, synthetic polymers, and porous clay
minerals are useful because of their large internal
surface area, stability, and low cost.
Activated carbon is the most common adsorbent
used in HVAC systems and portable air cleaners
to remove gaseous contaminants. It has the
potential to remove most hydrocarbons, many
aldehydes, and organic acids. However, activated
carbon is not especially effective against oxides of
sulfur, hydrogen sulfide, low
molecular weight aldehydes,
ammonia, and nitrogen oxide.
Chemisorption occurs
when gas or vapor molecules
chemically react with sorbent
material or with reactive agents
impregnated into the sorbent.
These impregnates react with
gases and form stable chemical
compounds that are bound
to the media as organic or inorganic salts, or
are broken down and released into the air as
carbon dioxide, water vapor, or some material
more readily adsorbed by other adsorbents.
Many different chemicals may be impregnated
on activated carbon; potassium permanganate
-------
A Summary of Available Information
is a common chemisorbent impregnated into
activated alumina. It reacts with many common
air pollutants, including formaldehyde and sulfur
and nitrogen oxides. Because a chemisorbent
will react with only one or a limited number of
reactive pollutants, it should not be expected to
reduce others.
Applications of Sorbents for Gaseous Pollutant
Removal
Gas-phase filters that contain sorbents may be
installed in HVAC systems or in portable air
cleaners. They are usually located downstream
of particle air filters. The air filter reduces the
amount of particulate matter that reaches the
sorbent, and the sorbent collects vapors that may
be generated from liquid particles that collect on
the particle filter.
Some gas-phase filters may remove, at least
temporarily, a portion of the gaseous pollutants in
indoor air. Although some gas-phase air filters—if
properly designed, used, and maintained—may
effectively remove specific pollutants from indoor
air, none is expected to remove adequately all
of the gaseous pollutants in a typical home. For
example, carbon monoxide is not readily captured
by adsorption or chemisorption. In addition,
gaseous-pollutant-removal systems usually have
a limited lifetime before the sorbent must be
replaced. There is also a concern
that saturated sorbent filters may
release trapped pollutants back
into the airstream.31
Tests of gaseous pollutant
removal by activated carbon
generally have been conducted
using only high concentrations of
pollutants, so little information is
available on carbon's effectiveness
in removing chemicals present in
the low concentrations (parts per
billion [ppb]) normally found in
indoor air. Tests performed at EPA measured the
adsorption isotherms for three volatile organic
compounds (VOCs) at concentrations of 100
ppb to 200 ppb using three samples of activated
carbon. The bed depth needed to remove the
EPA does not
recommend using
air cleaners to
reduce the health
risks associated
with radon.
compounds was estimated assuming a 150 ppb
concentration in the air, an exit concentration of
50 ppb, and a flow rate of 100 cfm across a
2' x 2' filter. The results of the study suggest that
breakthrough of these chemicals would occur
quickly in 6-inch deep carbon filters used for odor
control.32
Because of their compact design, particle air
filters that use impregnated media are available
for residential HVAC systems and portable air
cleaners. They use sorbent particles of carbon,
permanganate alumina, or zeolite incorporated
into fibrous filter media. Such filters generally
range from V8 inch to 2 inches thick. They
provide a combination of particulate and gas-
phase filtration with a minor increase in pressure
drop across the filter. Their use in an existing
HVAC system does not require extensive or
expensive modifications to the system. However,
their useful service life varies according to indoor
pollution concentrations and exposure time.
Breakthrough of the contaminants back into the
room takes place very quickly in the thin layer
impregnated with sorbents, resulting in a much
shorter service life for the filter, which must be
replaced frequently. Thus, these devices usually
have limited effectiveness in removing odors.
of Its
EPA does not recommend air
cleaning to reduce the health
risks associated with radon and
the decay products of radon gas,
which are called "radon progeny."
The Agency recommends the use
of source control technologies
to prevent radon from entering
residential structures. The most
effective radon control technique
is active soil depressurization
(ASD).1 An ASD system uses
an electric fan to minimize
radon entry by drawing air
from under the slab/floor and venting it to the
outside above the building's roofline. Another, less
effective technique installed during construction
is a passive radon reduction system, also known
as radon-resistant new construction (RRNC).
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RESIDENTIAL AIR CLEANERS
RRNC systems are "dual-purpose" systems. They
typically do not have a fan, but if subsequent
testing indicates an elevated radon level, a fan can
be installed and the RRNC system will become,
in effect, an ASD system.
A limited number of studies have investigated air
cleaners' effectiveness in removing radon and its
progeny. They compared the removal efficiencies
of various air cleaners, including mechanical air
filters, electrostatic precipitators, and ionizers
equipped with fans, and the risk reduction the
air cleaners achieve. However, the degree of risk
reduction found by these studies has
been inconsistent.
or of
Pollutants
Three types of air cleaners on the market are
designed to deactivate or destroy indoor air
pollutants: ultraviolet germicidal irradiation
(UVGI) cleaners, photocatalytic oxidation (PCO)
cleaners, and ozone generators sold as air cleaners.
Ultraviolet Germicidal Irradiation Cleaners
UVGI cleaners are intended to improve residential
lAQby deactivating indoor biological pollutants
that are airborne or growing on the moist interiors
of HVAC surfaces (e.g., cooling coils, drain pans,
or ductwork).
There is no standard test method to rate and
compare the effectiveness of UVGI cleaners
installed in either residential HVAC systems or
portable air cleaners. Typical UVGI cleaners used
in homes have limited effectiveness in killing
bacteria and molds. The effective destruction of
some viruses and most mold and bacteria spores
usually requires much higher UV exposures
than a typical home unit provides. Thus, UVGI
does not appear to be effective as a sole control
device. When UVGI is used, it should be used
in addition to—not as a replacement for—
conventional particle filtration systems.33 Using
UVGI in addition to HEPA filters in HVAC
systems or in portable units offers only minimal
infection control benefits over those provided by
the HEPA filters alone.33-34
Biological pollutants such as molds and
bacteria enter a house by various routes,
including open windows, joints and
cracks in walls, and on clothing, food,
or pets. Molds and some bacteria can
be found in either the vegetative or the
spore phase of their life cycle. Vegetative
bacteria and molds are in the growth and
reproductive phase; they are not spores.
Some bacteria form spores, an inactive
phase characterized by a thick protective
coating, to survive harsh environmental
conditions. Molds produce tiny spores
in order to reproduce. Mold spores will
germinate where moisture and nutrients
are available, such as on basement walls,
in refrigerators, on HVAC coils, on air
filters, and in drip pans.
Mechanical air filters will capture some
biological pollutants, but some will bypass
the filter along with the airstream, and
many small microorganisms can pass
through lower efficiency filter media.
Microorganisms such as bacteria and
molds also can enter the HVAC system by
the following mechanisms.
>• They may grow through the filter media
when conditions are favorable, for
example when moisture is present and
temperatures are high.34'35
>• They can be introduced into the system
during routine maintenance, for example
a filter change.36
>• Mold spores on the filters can be
released back to the airstream when
the air velocity suddenly increases, for
example during HVAC system startup or
off-and-on operation.37
Once bacteria and mold spores are
downstream of the filter, they may grow in
the presence of condensation on cooling
coils, drain pans, and internal thermal
insulation, or on the surfaces of the
air-handling unit and ductwork.
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A Summary of Available Information
UVGI Technology
Most UV lamps used to kill germs in residential
settings are low pressure mercury vapor lamps
that emit UV radiation at a wavelength of 253-7
nanometers, which has been shown to have
germicidal effects.38 UV light can penetrate the
outer structure of a microorganism's cell and alter
its DNA, permanently preventing replication and
causing cell death. But some bacterial and mold
spores are resistant to UV radiation.
Types of UVGI Their
Effectiveness
There are two types of UVGI applications:
cleaners designed for airstream disinfection, to
reduce the viability of microorganisms as they
flow through the HVAC system or portable
air cleaner, and cleaners designed for surface
disinfection, to prevent the reproduction of
microorganisms on specific components of an
HVAC system.38'39
UVGI lamps for airstream or surface disinfection
usually are located in the air duct of an HVAC
system downstream of the filter and upstream
of the cooling coil or in a portable air cleaner
downstream of the filter.
If properly designed, the UVGI cleaner in a
typical airstream disinfection application has
the potential to reduce the viability of vegetative
bacteria and molds and to provide low to moderate
reductions in viruses but little, if any, reduction in
bacterial and mold spores.33'34> 40
Spores tend to be resistant to UV
radiation, and killing them requires
a very high dosage.38'41> 42
When the fan in an airstream
disinfection application is
not operating, there is no air
movement and no disinfection.
UVGI cleaners might
not reduce allergy or
asthma symptoms.
UVGI cleaners in a surface disinfection
application are installed in air-handling units to
prevent or limit the growth of vegetative bacteria
and molds on moist surfaces in the HVAC
system.34'39'40'43 One study reported a 99-percent
reduction in microbial contaminants growing
on exposed HVAC surfaces, but a reduction in
airborne bacteria of only 25 to 30 percent.44 One
reason that the surface disinfection application
provides only a slightly noticeable reduction in
airborne microbial concentrations may be that
microorganisms in the airstream are exposed
to the UV light for a shorter time. Conversely,
microorganisms growing on exposed HVAC
surfaces are given prolonged direct UVGI
exposure. Another study found that UV lamps
yielded somewhat lower levels of mold in the
fiberglass insulation lining the air-handling unit.40
Prolonged direct UVGI exposure can destroy
vegetative microbial growth—but not most
spores—on the surfaces of forced-ventilation
units, filters, cooling coils, or drain pans. Killing
molds and bacteria while they are still in the
susceptible vegetative state reduces the formation
of additional spores. UV radiation is ineffective in
killing microorganisms if they proliferate inside
the filter media, system crevices, porous thermal
insulation, or sound-absorbing fibrous material
liners.39
A review of scientific literature has shown that
the effectiveness of UVGI cleaners in killing
microorganisms may vary depending on UV
irradiation dose, system design and application,
system operation characteristics, and the
microorganism targeted for deactivation. Further
independent testing using a standardized test
method is required before firmer conclusions can
be made about the effectiveness of
various UV cleaners in destroying
microorganisms of concern.
Some manufacturers of UVGI
cleaners used in HVAC systems
or portable air cleaners claim their
units reduce dust mite allergens,
airborne microorganisms such as
viruses, bacteria, molds, and their
spores, and gaseous pollutants from indoor air.
However, it is likely that the effective destruction
of some viruses and most mold and bacterial
spores requires much higher UV exposures than a
typical residential UVGI unit provides.36'38'39
19
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RESIDENTIAL AIR CLEANERS
No research or studies were found that show UV
disinfection is effective in reducing dust mite and
mold allergenicity or that UV radiation has the
potential to remove gaseous pollutants. Because
mold is allergenic, whether dead or alive, it can
cause allergic reactions in sensitive populations.
Therefore, UVGI cleaners might not be effective in
reducing allergy and asthma symptoms. If mold is
growing indoors, it should be removed.45
a UVGI
A number of studies 34>36>38>46>47 report that the
most important performance elements of a UVGI
system are the type of UV lamp and ballast, the
relative humidity, temperature, air velocity, and
duct reflectivity.
High output UV lamps have been found to
provide higher irradiance than low-output lamps.
Lamps designated for low-temperature operation
also appear to perform better. Increased relative
humidity is commonly believed to decrease the
irradiation of UVGI; however, the literature is
contradictory and incomplete. Air temperature
can affect the power output of UVGI lamps if it
exceeds design temperatures. Operating a UVGI
system at air velocity above
design will degrade the system's
effectiveness. Reflectivity
can be an economical way of
intensifying the UVGI field
in an enclosed duct. Polished
aluminum is highly reflective
of UV wavelengths, while
typical duct liner material has
little or no reflectance in the
UV spectrum.
Application of
PCO cleaners for
homes is limited in
destroying gaseous
pollutants from
indoor air.
Regular maintenance of
UVGI systems is crucial and usually consists of
cleaning the lamps of dust and replacing old lamps.
Manufacturers' recommendations regarding safety
precautions, exposure criteria, maintenance, and
monitoring associated with the use of UVGI
systems should be followed.
By-products by UVGI
According to two studies,38'43 operating UV lamps
installed in HVAC systems to irradiate the surfaces
of air-handling units does not result in increased
concentrations of ozone, VOCs, or other chemical
by-products.
Photocatalytic Oxidation Cleaners
PCO cleaners are intended to destroy gaseous
pollutants and their odors by converting them
into harmless products, but they are not designed
to remove particulate pollutants. PCO cleaners
use a UV lamp and a photocatalyst, usually
titanium dioxide, to create oxidants that destroy
gaseous contaminants. When the photocatalyst
is irradiated with UV light, a photochemical
reaction takes place and hydroxyl radicals form.
The hydroxyl radicals oxidize gaseous pollutants
adsorbed on the catalyst surface. This reaction,
called photocatalytic oxidation, converts organic
pollutants into the carbon dioxide and water.
To achieve effective conversion, the reaction
rate of the PCO cleaner must match the rates
of contaminant generation and infiltration rate
minus the exfiltration rate (movement of the air
from the space served to the outdoors).
There is no standard test method to compare and
rate the effectiveness of PCO cleaners installed
in residential HVAC systems or
portable air cleaners. PCO is an
emerging technology intended
to improve residential lAQby
destroying gaseous contaminants.
Although PCO is still under
development, a few home air
cleaners that use it are available in
the United States. PCO cleaners are
promoted for use in HVAC system
ducts or in portable air cleaners.
Some manufacturers claim PCO
devices can remove tobacco smoke,
microorganisms, and other indoor particulate
pollutants even though the devices are not meant
to remove particles.
The usefulness of PCO cleaners in homes is
limited because available photocatalysts (i.e.,
substances that react with light) are ineffective
in completely destroying gaseous pollutants
in indoor air.48>49>5° Other application and
engineering issues are not fully resolved,
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A Summary of Available Information
including the relatively large power consumption
of PCO units; the complexity of the PCO
process, which combines the operation of a UV
light and a catalyst; and the need to remove
multiple compounds from the contaminated
airstream. Some PCO cleaners fail to destroy
pollutants completely and instead produce new
indoor pollutants that may cause irritation of the
eyes, throat, and nose. Until more data become
available, information on the performance of PCO
cleaners will remain limited and inconclusive.
of PCO
One study 51 reported that PCO devices installed
in portable air cleaners did not effectively
remove any of the test VOCs present at the low
concentrations normally found in indoor air. This
study compared the VOC-removal efficiencies
of 15 air cleaners that use
different types of technology.
A mixture of 16 VOCs
commonly found indoors
was used. The report
indicated that the PCO
devices studied might not
work as advertised. The
findings also showed that
some devices appear not to
have fully implemented PCO technology.
A review of the literature suggests that more
research is needed to further advance PCO as
an effective technology in removing low levels
of gaseous contaminants from the indoor air
of residences.49'50'51 This additional research
should include many important performance
characteristics that influence the effectiveness of
PCO cleaners, such as whether:
l> A decrease in light irradiance with illumination
time inhibits performance.49
l> Photocatalyst deactivation in the presence of
chemicals such as toluene, benzene, ethanol, or
hexamethyldisilazane decreases performance.
49, 50,52
^ An increase in reaction temperature or water
vapor content increases the PCO reaction
Ozone is a lung
irritant that can
cause adverse health
effects.
rate.
53
^ Competitive adsorption between gaseous
contaminants affects the PCO reaction
mechanism.49'54
Estimated costs of PCO technology are significantly
higher than those of activated carbon technology. A
major factor influencing PCO costs is the intensity
of UV light required at the inlet to destroy a range
of VOCs at the low concentrations that typify IAQ
problems.48
PCO By-products
PCO of certain VOCs may create by-products
that are indoor pollutants if the system's design
parameters and catalyst metal composition do not
match the compound targeted for decomposition,
particularly in the presence of multiple reactive
compounds commonly found in residential settings.
One study reported that no detectable
by-products formed during the PCO of
17 VOCs using titanium dioxide under
the experimental conditions.55 However,
two studies on the degradation of 4
chlorinated VOCs found by-products
including phosgene and chlorides.56'57 In
addition, the PCO of trichloroethylene
in air using titanium dioxide as the
catalyst yielded as by-products carbon
monoxide, phosgene, carbon dioxide, hydrogen
chloride, and chlorine.
Ozone Generators
Ozone generators sold as air cleaners and marketed
as in-duct or portable units use UV light or corona
discharge to produce ozone, which is dispersed by a
fan into occupied spaces.8
Some manufacturers and vendors of ozone
generators suggest that ozone reacts with both
chemical and biological pollutants and transforms
them into harmless substances. They also often
make statements and distribute materials that
lead the public to believe that these devices are
always safe and effective in controlling indoor air
pollutants. However, ozone is an irritant gas that
reacts with lung tissue and can cause asthma attacks;
coughing; chest discomfort; irritation of the nose,
throat, and trachea; and other adverse health effects.
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RESIDENTIAL AIR CLEANERS
As ozone reacts with chemical pollutants, it can
produce harmful by-products.8'9l 10
Available scientific evidence shows that, at ozone
concentrations below public health standards,
ozone has little potential to remove indoor
air contaminants such as many odor-causing
chemicals, viruses, bacteria, molds, and tobacco
smoke; thus, ozone is generally ineffective in
controlling indoor air pollution. Some controlled
studies show that the concentration of ozone
produced by ozone generators can exceed
standards even when consumers follow the
manufacturer's instructions. No federal agency
has approved ozone generators for use in occupied
spaces.
There is a large body of written material
on ozone and the use of ozone indoors, but
much of this material makes claims or draws
conclusions without substantiation and a basis in
sound science. In developing Ozone Generators
that Are Sold as Air Cleaners, EPA reviewed a
wide assortment of this literature, including
information provided by a leading manufacturer
of ozone-generating devices. In keeping with
EPA's policy of ensuring that the information
it provides is based on sound science, only peer
reviewed, scientifically supported findings and
conclusions were relied on in developing this
document. The document is posted on the EPA
Web site at wwAyja:^^
The public is advised to use methods proven to
be safe and effective in controlling indoor air
pollution. These methods include eliminating
or controlling pollutant sources and increasing
outdoor air ventilation.
Federal pesticide law requires manufacturers of
ozone generators to list an EPA establishment
number on the product's packaging. This number
merely identifies the facility that manufactured
the product. The presence of this number on a
product's packaging does not imply that EPA
endorses the product, nor does it imply that EPA
has found the product to be safe or effective.
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A Summary of Available Information
Air-cleaning devices may help reduce levels of
smaller airborne allergens, particles, or, in some
cases, gaseous pollutants in a home. However, air
cleaners may not decrease adverse health effects
particularly in sensitive populations such as
children, people with asthma and allergies, and
the elderly.
Clinicians frequently recommend that patients
who have asthma or allergies use HEPA air filters
in HVAC systems or in portable air cleaners.
Regardless of how efficient and effective air-
cleaning devices are in removing pollutants, a
question still remains about their ability to reduce
adverse health effects.
How effectively air-cleaning devices alleviate
allergic and other health symptoms remains
uncertain. Strong data linking air-cleaning
devices to reduced health symptoms do not
exist. Many studies have associated air-cleaning
devices with reductions in airborne indoor
pollutant concentrations, but more clinical studies
are needed to determine whether air cleaners
significantly affect health outcomes. A literature
review documented only a limited number of
studies that attempted to evaluate the clinical
outcomes of air cleaner use. These studies focused
on more sensitive groups, such as asthmatic and
allergic individuals, children, and the elderly. A
number of the studies had important limitations,
such as small study size, short duration, and
lack of blinding (i.e., subjects and scientists were
aware of air cleaner operation), which may result
in a placebo effect. The results were also more
suggestive than conclusive.
Many indoor pollutants related to asthma and
allergies are either airborne particles or irritants,
such as the gaseous components of secondhand
smoke or nitrogen dioxide, chemicals linked
with gas cooking appliances, fireplaces, wood
stoves, and unvented kerosene and gas space
heaters. Most studies involving subjects who
have perennial and seasonal allergy or asthma
symptoms tested portable air cleaners equipped
with HEPA filters.
Few studies tested gas-phase filtration and air
cleaners using UV light technology, such as UVGI
cleaners and PCO cleaners. The scarcity of data
results in little scientific evidence that these devices
are associated with a reduction in health symptoms.
The effects of particle air cleaners on allergy
and asthma symptoms have been reviewed by
the Institute of Medicine (IOM) Committee
on the Assessment of Asthma and Indoor Air of
the National Academy of Sciences.26 The IOM
concluded that:
The results of existing experimental studies are
inadequate to draw firm conclusions regarding
the benefits of air cleaning for asthmatic
and allergic individuals— Air cleaners are
helpful in some situations in reducing allergy
or asthma symptoms, particularly seasonal
symptoms, but it is clear that air cleaning, as
applied in the studies, is not consistently and
highly effective in reducing symptoms.
The use of air cleaners may help reduce levels of
smaller airborne allergens or particles, but should
not be expected to effectively reduce health
symptoms.
Several factors should be considered in evaluating
whether an air cleaner is beneficial in alleviating
health effects.
^ Many studies on the health benefits of air
cleaning involve multiple interventions and
thus are not useful in determining the effects of
air cleaners alone.
The health benefits of air cleaners are often
studied along with other interventions such as
mattress and pillow covers, exclusion of pets
from the bedroom, weekly baths for pets, or
vacuum cleaning. Studies that consider air
cleaning concurrently with other interventions
have relatively little value in determining
the clinical outcome resulting from the use
II
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RESIDENTIAL AIR CLEANERS
of air cleaners because it is not clear if any
improvements demonstrated are due to
the air-cleaning devices or to the other
73 74 75 77 78 58 59
interventions. 3- • 5> '• '5 ' ^
An air cleaner's ability to
remove some airborne
pollutants, including
microorganisms, is not,
in itself, an indication of
the air cleaner's ability to
reduce health symptoms.
An air cleaner's ability
to remove some
airborne pollutants is
not an indication of
its ability to reduce
health symptoms.
As discussed previously,
pollen, dust mite and
cockroach allergens, some mold spores, and
animal dander carried on large particles
settle rapidly before they can be removed
by filtration. Because these particles do not
remain airborne, air-cleaning devices are
relatively ineffective in their removal.q>26>60
Therefore, effective allergen control requires
routine cleaning and dust control including
the weekly washing of bed sheets, frequent
vacuuming of carpets and furniture, and
regular dusting and cleaning of hard surfaces.
(For more on allergen control, visit
effectiveness of UVGI cleaners in reducing
health symptoms in either airstream or surface
applications. Despite UVGI's ability to
deactivate some surface-grown microorganisms,
data linking the effectiveness of UVGI
systems to reduced health symptoms in
sensitive populations such as children,
asthmatic and allergic individuals,
and the elderly are not available for
residential settings.
l» Some air cleaners may produce
new, potentially toxic pollutants or may
re-disperse old ones.
A significant fraction of cat and dog allergens
and a small portion of dust mite allergens
associated with mite feces are carried on
small particles. Consequently, they are more
easily dispersed throughout a house, remain
airborne longer, and are more likely to be
removed by air cleaners.23'61 Although there
is evidence that some air cleaners can remove
a portion of smaller particles from the air,
there is little evidence that these reductions
in particle levels alleviate
health symptoms. This lack
of improvement in symptoms
may be due in part to the fact
that, once sensitized, allergic
and asthmatic individuals
respond to much lower levels
of pollutants.
There is little clinically
confirmed support for the
Air cleaning may have
a useful role when
used in conjunction
with source control
and ventilation with
clean outdoor air.
A limited number of studies report that
irradiation by UVGI lamps reduce vegetative
bacteria and molds that are either airborne or
growing on moist HVAC surfaces.34'39'40'43'44
However, the dead mold spores may still cause
allergic reactions in some people.
High moisture and elevated temperatures
can promote bacteria and mold growth in
particulate filter media.35 Air filters may re-
emit bacteria and mold spores during HVAC
startup and off-and-on operations when air
velocity suddenly increases.37
Ozone generators sold as air cleaners for use in
occupied indoor spaces produce ozone, a lung
irritant.8 Electronic air cleaners, such as ion
generators and electrostatic precipitators, have
the potential to emit potentially dangerous
levels of ozone.5'22'29 Contamination of
electrode surfaces in electronic air cleaners
may cause increased ozone levels.62 There also
have been reports of electronic air cleaners
producing fine particulate material from the
reaction of ozone produced in
the corona discharge with other
chemicals indoors.9'10'63
Liquid tobacco smoke particles
trapped by an air filter may give
off odorous organic gases.12
Saturated sorbent filters may also
release trapped gaseous pollutants
back into the airstream.31 If a
PCO system's design parameters
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A Summary of Available Information
do not match the pollutant targeted for
decomposition, the PCO cleaner may create,
as a result of the oxidation process of certain
VOCs in indoor air, by-products that are
indoor air pollutants.
Current evidence suggests that air cleaning
may have a useful role when used in
conjunction with source control and
ventilation with clean outdoor air.
Several factors other than the ability of air-
cleaning devices to reduce airborne pollutant
concentrations should be considered when
deciding whether to use air cleaners.
In-duct air-cleaning devices require sufficient
access for inspection during use, repair, and
maintenance. Electronic air cleaners and UV
lamps should have an accessible power supply
and an indicator showing when electrical service
is off. The installation of UV lamps requires
the addition of access holes into the duct, and
the holes must be properly sealed to maintain
HVAC efficiency. Mechanical air filters should
be installed so that the directional arrow printed
on the side of the filter points in the direction of
airflow within the system. Incorrectly designed
or installed filter frames can cause air seepage,
which significantly decreases filter effectiveness.
High efficiency filters require well sealed frames
to prevent leaks. Installing a higher efficiency
and HEPA filter would probably require sheet
metal modifications to the existing ductwork to
permit the installation of the thicker air cleaner.
In addition, a more powerful fan often must be
installed to overcome the higher pressure drop.
In some cases, consumers have been left with
no useful manufacturer's instructions that
recommend replacement of various air-cleaning
devices over their lifetime other than the general
manufacturer's operating and maintenance
procedures to be followed to ensure adequate
air cleaner performance. Air cleaners should be
selected to match operating conditions, such as
degree of air cleanliness needed, type of pollutant
to be removed, and allowable pressure drop. A fan
that has sufficient capacity (pressure and airflow
ratings) to move air through the filter media must
also be included.
Filters and sorbents must be replaced, and the
plates or charged media of electronic air cleaners
must be cleaned. Electronic air cleaner efficiency
decreases as the collecting plates become loaded
with particles, so the plates must be cleaned,
sometimes frequently, as required by the
manufacturer. The cleanings should be scheduled
to keep the unit operating at peak efficiency.
Special attention must be given to cleaning the
ionizing wires of electronic air cleaners designed
to target certain contaminants.
During cleaning or replacement of air cleaners, an
effort should be made to ensure that pollutants are
not re-emitted into the air. For example, excessive
movement or air drafts should be avoided when
filters are removed. Used filters should be placed
in plastic bags or other containers for disposal.
To avoid electrical and mechanical hazards,
consumers should make sure air-cleaning devices
that require an electrical power supply are listed
on the Underwriters Laboratories Web site
at www.ul.corn or with another recognized
independent safety testing laboratory.
Cost
Cost may also be a consideration. Major costs
include the initial purchase price, maintenance
(such as cleaning or replacing filters and parts),
and operation (such as electricity).
The most effective air cleaners—those with
high airflow rates and efficient particle capture
systems—generally are the most costly.
Maintenance costs vary depending on the device,
and these costs should be considered when
choosing a particular unit. Operating cost is as
important as purchase cost because air cleaning
11
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RESIDENTIAL AIR CLEANERS
is a continuing process. The cost of professional
installation of an electronic air filter or a
HEPA filter in the HVAC system must also be
considered. Consumers should consider obtaining
information on purchase and annual operating
costs for various products from Consumer Reports
magazine and other sources.
to
Air-cleaning devices designed to remove particles
are incapable of controlling gases and some
odors. For example, the odor and many of the
carcinogenic gas-phase pollutants from tobacco
smoke will remain in filtered air. Particles of liquid
tobacco smoke trapped by an air filter may give
off odorous organic gases.12
of
Another factor to consider related to ion
generators is the effect of particle charging on
deposition in the respiratory tract. Experiments
have shown that particle deposition increases with
charge, so using ion generators may not reduce
the dose of particles to the lungs.63'64 The effect of
charge on very fine particles results in their higher
deposition rate in the lungs compared to that of
uncharged particles.
Ion generators generally are not designed to
remove from the air the charged particles that they
generate. These charged particles deposit on and
soil room surfaces such as walls and curtains.63'64
Consequently, there is no true effective removal of
the particles from the space. Deposited particles,
especially those larger than approximately 2 um,
may be re-suspended from the surfaces when
disturbed by human activities such as walking
or vacuuming.
Noise may also be a consideration in selecting a
portable air cleaner that contains a fan. Portable
air cleaners that do not have fans typically are
much less effective than units that have them. In
tests by Consumers Union, the largest portable air
cleaners were the noisiest on their most effective
high speed settings.65 However, some performed
more quietly at low speed than many smaller
cleaners do on high. Some larger portable units
operating at low speed were found to be quiet
enough for most households.22
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A Summary of Available Information
Indoor air pollution is among the top five environmental risks to public health. The best way to address
this risk is to control or eliminate the sources of pollutants and to ventilate a home with clean outdoor
air. The ventilation method, however, may be limited by weather conditions or undesirable levels of
contaminants in outdoor air. If these measures are insufficient, an air-cleaning device may be useful.
While air-cleaning devices may help control the levels of airborne particles including those associated
with allergens and, in some cases, gaseous pollutants in a home, air cleaning may not decrease adverse
health effects from indoor air pollutants.
This document was prepared to provide housing design professionals, public health officials, and indoor
air quality professionals with useful information on the available types of air-cleaning devices and their
overall effectiveness in reducing air pollutants and associated health impacts. It is important to remember
that there is no scientific evidence that shows air-cleaning devices to be consistently and highly effective
in reducing adverse health effects from indoor air pollutants.
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RESIDENTIAL AIR CLEANERS
Acute
Adsorption
Air cleaner
Air filter
Airflow resistance
Allergen
Allergic respiratory disease
Allergy
Asthma
Bacterial spore
CADR
Chemisorption
Chronic
Corona discharge
Dander
Disinfection
Double-blind study
Having a rapid onset and following a short but potentially severe course.
The physical process that occurs when liquids, gases, or suspended matter adhere to
the surfaces or in the pores of a material.
A device used to remove particulate or gaseous impurities from the air; examples
include electrostatic precipitator, ion generator, ultraviolet germicidal irradiation
cleaner, photocatalytic oxidation cleaner, and gas-phase air filter.
A device that removes particulate material from an airstream, also called an "air
cleaner."
See Pressure drop.
A chemical or biological substance (e.g., pollen, animal dander, or house dust mite
proteins) that can cause an allergic reaction characterized by hypersensitivity (an
exaggerated response).
Impairment of the normal state of the respiratory system resulting from exposure—
usually by inhalation—to an allergen.
An exaggerated or pathological reaction to breathing, eating, or touching substances
that have no comparable effect on the average individual.
A usually chronic inflammatory disorder of the airways characterized by intermittent
episodes of wheezing, coughing, and difficulty breathing, sometimes associated with
an allergy to inhaled substances.
Inactive phase of bacteria, with a thick protective coating that allows the bacteria to
survive harsh environmental conditions.
The Clean Air Delivery Rate (CADR) is the measure of portable room air cleaner
performance. This is defined as the measure of the delivery of contaminant-free air by a
portable household electric room air cleaner, expressed in cubic feet per minute (cfm).
CADRs are always the measurement of a unit's performance as a complete system.
A process whereby a chemical substance adheres to a surface through the formation
of a chemical bond.
Marked by long duration, by frequent recurrence over a long time, and often by
slowly progressing seriousness.
An electrical discharge brought on by the ionization of a fluid surrounding a
conductor, which occurs when the potential gradient exceeds a certain value.
Minute scales of skin. Dander also may contain hair or feathers.
The process of any reduction or prevention of growth in a microbial population with
no percentage efficiency specified.
A type of clinical trial study design in which the study participants and the
investigators do not know the identity of the individuals in the intervention and
control groups until data collection has been completed.
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A Summary of Available Information
HEPA filter
HVAC
IAQ
MERV
Mold spore
Ozone
Paniculate
PCO
Placebo effect
Pressure drop
Rhinitis
Sorption
ULPA
UV
UVGI
VOCs
Vegetative bacteria
and molds
High-efficiency particulate air filter. Extended surface mechanical air filter having
a minimum particle removal efficiency of 99-97 percent for all particles of 0.3 um
diameter, with high efficiency for both larger and smaller particles.
Heating, ventilating, and air conditioning.
Indoor air quality.
Minimum efficiency reporting value.
Tiny reproductive structures produced by vegetative mold.
An unstable, poisonous allotrope of oxygen that is formed naturally in the ozone
layer from atmospheric oxygen by electric discharge or exposure to ultraviolet
radiation, also produced in the lower atmosphere by the photochemical reaction of
certain pollutants.
A small discrete mass of solid or liquid matter that remains individually dispersed in
gas or liquid emissions (usually considered to be an atmospheric pollutant).
Photocatalytic oxidation.
A usually, but not necessarily, beneficial effect attributable to an expectation that a
treatment will have an effect; an effect that is due to the power of suggestion; a sense
of benefit felt by a patient that arises solely from the knowledge that treatment has
been given.
The loss offeree applied over a filtering media surface due to resistance to airflow.
Inflammation of the mucous membrane lining of the nose.
The common term used for adsorption.
Ultra low penetration air filter. Extended surface mechanical air filter having a
minimum particle removal efficiency of 99-999 percent for all particles of 0.3 um
diameter, with high efficiency for both larger and smaller particles.
Ultraviolet.
Ultraviolet germicidal irradiation.
Volatile organic compounds; chemicals that contain carbon and are vaporous at room
temperature and pressure.
Microorganisms that are in the growth and reproductive phase, i.e., not spores.
ii
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RESIDENTIAL AIR CLEANERS
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A Summary of Available Information
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A Summary of Available Information
Visit our Web site for any additional information about indoor air quality at http://wwWiega.gov/iag.
An electronic copy of this document Residential Air Cleaners (Second Edition) A Summary of Available Information,
EPA 402-F-09-002, August 2009, is available at
An electronic copy of the EPA brochure Guide to Air Cleaners in the Home, EPA 402-F-08-004, May 2008,
addressed to the general public is available at
For hard copies of Guide to Air Cleaners in the Home and other EPA indoor air publications, contact:
National Service Center for Environmental Publications (NSCEP)
P.O. Box 4241 9
Cincinnati, OH 424 19
phone: (800) 490-9198
fax: (301) 604-3408
Web site:Jittg://www.ega.gav/nsceD
Residential Air-Cleaning Devices — Types, Effectiveness and Health Impact. American Lung Association.
Web site: Httg^//wwwjujigusa.org
Air-Cleaning Devices for the Home, Frequently Asked Questions. California Air Resources Board and the California
Environmental Protection Agency.
Web site: ]ltt|3i£/_www^^
Survey of the Use of Ozone-generating Air Cleaners by the California Public. California Air Resources Board and the
California Environmental Protection Agency, January 2007-
Web site:
Hodgson, A.T., Hugo Destaillats, H., Hotchi, T, Fisk, WJ. 2007- Evaluation of a Combined Ultraviolet
Photocatalytic Oxidation (UVPCO)/Chemisorbent Air Cleaner for Indoor Air Applications. Lawrence Berkeley
National Laboratory. Paper LBNL-62202.
Hodgson, A.T., Sullivan, D.P, Fisk, WF. September 30, 2005- Evaluation of Ultra- Violet Photocatalytic Oxidation
(UVPCO) for Indoor Air Applications: Conversion of Volatile Organic Compounds at Low Part-per-Billion
Concentrations. Lawrence Berkeley National Laboratory. Paper LBNL-58936.
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