United States
Environmental Protection
Agency
Air Cleaners
in the Home
-------
Please Note: 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 performance
characteristics associated with
several types of air cleaners sold to
consumers for home use. It does
not discuss the effectiveness of air
cleaners installed in the HVAC
systems of large buildings, such
as apartments, offices, schools, or
public buildings.
Under Federal pesticide law,
manufacturers of ozone generators
must list an EPA establishment
number on the packaging. This
number merely identifies the
facility that manufactured the
product. Display of this number
implies neither EPA endorsement
nor that EPA has found the
product to be safe or effective.
Some portable air cleaners sold in
the consumer market are ENERGY
STARฎ 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."
Introduction
Indoor air pollutants are unwanted, sometimes harmful
materials in the air. 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 to ventilate a home with clean outdoor air.
The ventilation method may, however, be limited by weather
conditions or undesirable levels of contaminants contained in
outdoor air. If these measures are insufficient, an air cleaning
device may be useful. Air cleaning devices are intended to
remove pollutants from indoor air. Some air cleaning devices
are designed to be installed in the ductwork of a home's
central heating, ventilating, and air-conditioning (HVAC)
system to clean the air in the whole house. Portable room
air cleaners can be used to clean the air in a single room or
specific areas, but they are not intended for whole-house
filtration. The following pages will provide information on
different types of air cleaning devices and how they work.
-------
Guide to Air Cleaners in the Home
Indoor Air Pollutants
Pollutants that can affect air quality in a home fall into the following categories:
> Paniculate matter includes dust, smoke, pollen, animal dander, tobacco smoke, particles generated from combustion
appliances such as cooking stoves, and particles associated with tiny organisms such as dust mites, molds, bacteria,
and viruses.
* Gaseous pollutants come from combustion processes. Sources include gas cooking stoves, vehicle exhaust, and to-
bacco smoke. They also come from building materials, furnishings, and the use of products such as adhesives, paints,
varnishes, cleaning products, and pesticides.
Understanding the
Types of Air Cleaning
Devices
Before deciding whether to use an air
cleaning device, several questions should
be considered:
> What types of pollutants can an air
cleaner remove?
> How is the performance of an air
cleaner measured?
> Will air cleaning reduce adverse health
effects?
> What other factors should I consider?
These questions will be addressed in the
next few pages.
What Types of Pollutants Can an
Air Cleaner Remove?
There are several types of air cleaning devices available, each
designed to remove certain types of pollutants.
Particle Removal
Two types of air cleaning devices can remove particles from the
airmechanical air filters and electronic air cleaners. Mechanical
air filters remove particles by capturing them on filter materials.
High efficiency particulate air (HEPA) filters are in this category.
Electronic air cleaners such as electrostatic precipitators use a process
called electrostatic attraction to trap charged particles. They draw
air through an ionization section where particles obtain an electrical
charge. The charged particles then accumulate on a series of flat
plates called a collector that is oppositely charged. Ion generators, or
ionizers, disperse charged ions into the air, similar to the electronic
air cleaners but without a collector. These ions attach to airborne
particles, giving them a charge so that they attach to nearby surfaces
such as walls or furniture, or attach to one another and settle faster.
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
Gaseous Pollutant Removal
Gas-phase air filters remove gases and odors by using a material called a sorbent, such as activated carbon, which
adsorbs the pollutants. These filters are typically intended to remove one or more gaseous pollutants from the airstream
that passes through them. Because gas-phase filters are specific to one or a limited number of gaseous pollutants, they
will not reduce concentrations of pollutants for which they were not designed. Some air cleaning devices with gas-
phase filters may remove a portion of the gaseous pollutants and some of the related hazards, at least on a temporary
basis. However, none are expected to remove all of the gaseous pollutants present in the air of a typical home. For
example, carbon monoxide is a dangerous gaseous pollutant that is produced whenever any fuel such as gas, oil,
kerosene, wood, or charcoal is burned, and it is not readily captured using currently available residential gas-phase
filtration products.
Pollutant Destruction
Some air cleaners use ultraviolet (UV) light technology intended to destroy pollutants in indoor air. These air cleaners
are called ultraviolet germicidal irradiation (UVGI) cleaners and photocatalytic oxidation (PCO) cleaners. Ozone
generators that are sold as air cleaners intentionally produce ozone gas, a lung irritant, to destroy pollutants.
> UVGI cleaners use ultraviolet radiation from UV lamps that may destroy biological pollutants such as viruses,
bacteria, allergens, and molds that are airborne or growing on HVAC surfaces (e.g., found on cooling coils, drain
pans, or ductwork). If used, they should be applied with, but not as a replacement for, filtration systems.
* PCO cleaners use a UV lamp along with a substance, called a catalyst, that
reacts with the light. They are intended to destroy gaseous pollutants by
converting them into harmless products, but are not designed to remove
particulate pollutants.
* Ozone generators use UV light or an electrical discharge to intentionally
produce ozone. Ozone is a lung irritant that can cause adverse health effects. At
concentrations that do not exceed public health standards, ozone has little effect
in removing most indoor air contaminants. Thus, ozone generators are not
always safe and effective in controlling indoor air pollutants. Consumers should
instead use methods proven to be both safe and effective to reduce pollutant
Ozone is a
lung irritant
that can cause
adverse health
effects.
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
concentrations, which include eliminating or controlling pollutant sources and increasing outdoor air
ventilation. Visit www.epa.gov/iaq/pubs/ozonegen.html for more information on ozone generators
sold as air cleaners.
The chart below provides a brief summary of air cleaning technologies and the pollutants they are
designed to control.
AIR CLEANING
TECHNOLOGIES
Filtration
Other Air
Cleaners
Air filters
Gas-phase
filters
UVGI
PCO
Ozone
generators
POLLUTANTS
ADDRESSED
Particles
Gases
Biologicals
Gases
Particles, gases,
biologicals
LIMITATIONS
Ineffective in removing larger particles because most settle from
the air quickly and never reach filters.
Used much less frequently in homes than particle air filters. The
lifetime for removing pollutants may be short.
Bacterial and mold spores tend to be resistant to UV radiation
and require more light or longer time of exposure, or both, to be
killed.
Application for homes is limited because currently available
catalysts are ineffective in destroying gaseous pollutants from
indoor air.
Sold as air cleaners, they are not always safe and effective in
removing pollutants. By design they produce ozone, a lung irritant.
In addition to understanding the different types of air cleaning devices, consumers should consider
their performance, as explained in the next section.
REMINDERS
HVAC
Heating,
ventilating, and
air-conditioning
PCO
Photocatalytic
oxidation
UV
Ultraviolet
UVGI
Ultraviolet
germicidal
irradiation
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
How is the Performance of an Air Cleaner Measured?
There are different ways to measure how well air cleaning devices work, which depend on the type of device and the
basic configuration. Air cleaning devices are configured either in the ductwork of HVAC systems (i.e., in-duct) or as
portable air cleaners.
In-duct Particle Removal
Most mechanical air filters are good at capturing larger airborne particles, such as dust, pollen, dust mite and
cockroach allergens, some molds, and animal dander. However, because these particles settle rather quickly, air filters
are not very good at removing them completely from indoor areas. Although human activities such as walking and
vacuuming can stir up particles, most of the larger particles will resettle before an air filter can remove them.
Consumers can select a particle removal air filter by looking at its efficiency in removing airborne particles from the
air stream that passes through it. This efficiency is measured by the minimum efficiency reporting value (MERV)
for air filters installed in the ductwork of HVAC systems. The American Society of Heating, Refrigerating and Air-
Conditioning Engineers (ASHRAE) developed this measurement method. MERV ratings (ranging from a low of 1 to
a high of 20) also allow comparison of air filters made by different companies.
* Flat or panel air filters with a MERV of 1 to 4 are commonly used in residential furnaces and air conditioners.
For the most part, such filters are used to protect the HVAC equipment from the buildup of unwanted materials
on the surfaces such as fan motors and heating or cooling coils, and not for direct indoor air quality reasons. They
have low efficiency on smaller airborne particles and medium efficiency on larger particles, as long as they remain
airborne and pass through the filter. Some smaller particles found within a house include viruses, bacteria, some
mold spores, a significant fraction of cat and dog allergens, and a small portion of dust mite allergens.
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
Pleated or extended surface filters
Medium efficiency filters with a MERV of 5 to 13 are
reasonably efficient at removing small to large airborne
particles. Filters with a MERV between 7 and 13 are likely
to be nearly as effective as true HEPA filters at controlling
most airborne indoor particles. Medium efficiency air filters
are generally less expensive than HEPA filters, and allow
quieter HVAC fan operation and higher airflow rates than
HEPA filters since they have less airflow resistance.
Higher efficiency filters with a MERV of 14 to 16,
sometimes misidentified as HEPA filters, are similar in
appearance to true HEPA filters, which have MERV values
Filters with a
MERV between 7
and 13 are likely
to be nearly as
effective as true
HEPA filters.
of 17 to 20. True HEPA filters are normally not installed
in residential HVAC systems; installation of 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 physical
dimensions and increase in airflow resistance.
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. Specially
built high performance homes may occasionally be equipped with true HEPA filters installed in a
properly designed HVAC system.
There is no standard measurement for the effectiveness of electronic air cleaners. While they may
remove small particles, they may be ineffective in removing large particles. Electronic air cleaners can
produce ozone a lung irritant. The amount of ozone produced varies among models. Electronic air
cleaners may also produce ultrafine particles resulting from reaction of ozone with indoor chemicals
such as those coming from household cleaning products, air fresheners, certain paints, wood flooring, or
carpets. Ultrafine particles may be linked with adverse health effects in some sensitive populations.
REMINDERS
ASHRAE
American Society
of Heating,
Refrigerating and
Air-Conditioning
Engineers
HEPA
High efficiency
participate air
HVAC
Heating,
ventilating, and
air-conditioning
MERV
Minimum
efficiency
reporting value
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
In-duct Gaseous Pollutant Removal
Although there is no standard measurement for the effectiveness of gas-phase air filters, ASHRAE is developing a
standard method to be used in choosing gas-phase filters installed in home HVAC systems. Gas-phase filters are much
less commonly used in homes than particle air filters. The useful lifetime of gas-phase filters can be short because the
filter material can quickly become overloaded and may need to be replaced often. There is also concern that, when full,
these filters may release trapped pollutants back into the air. Finally, a properly designed and built gas-phase filtration
system would be unlikely to fit in a typical home HVAC system or portable air cleaner.
In-duct Pollutant Destruction
There is no standard measurement for the effectiveness of UVGI cleaners. 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 exposure than is provided in a typical home
unit. Furthermore, dead mold spores can still produce allergic reactions, so UVGI
cleaners may not be effective in reducing allergy and asthma symptoms.
There is no standard measurement for the effectiveness of PCO cleaners. The
use of PCO cleaners in homes is limited because currently available catalysts are
ineffective in destroying gaseous pollutants from indoor air. Some PCO cleaners
fail to destroy pollutants completely and instead produce new indoor pollutants
that may cause irritation of the eyes, throat, and nose.
UVGI cleaners
may not
reduce allergy
or asthma
symptoms.
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
Portable Air Cleaners
Portable air cleaners generally contain a fan to circulate the air and use one or more of the air cleaning
devices discussed above. Portable air cleaners may be moved from room to room and used when
continuous and localized air cleaning is needed. They may be an option if a home is not equipped with a
central HVAC system or forced air heating system.
Portable air cleaners can be evaluated by their effectiveness in reducing airborne pollutants. This
effectiveness is measured by the clean air delivery rate (CADR) developed by the Association of Home
Appliance Manufacturers (AHAM). The CADR is a measure of a portable air cleaner's delivery of
contaminant-free air, expressed in cubic feet per minute. For example, if an air cleaner has a CADR of
250 for dust particles, it may reduce dust particle levels to the same concentration as would be achieved
by adding 250 cubic feet of clean air each minute. While a portable air cleaner may not achieve its rated
CADR under all circumstances, the CADR value does allow comparison across different portable air
cleaners.
Many of the portable air cleaners tested by AHAM have moderate to large CADR ratings for small
particles. However, for typical room sizes, most portable air cleaners currently on the market do not have
high enough CADR values to effectively remove large particles such as pollen, dust mite, and cockroach
allergens. Some portable air cleaners using electronic air cleaners might produce ozone, which is a lung
irritant. AHAM has a portable air cleaner certification program, and provides a complete listing of all
certified cleaners with their CADR values on its Web site at www.cadr.org.
REMINDERS
AHAM
Association of
Home Appliance
Manufacturers
CADR
Clean air delivery
rate
ASHRAE
American Society
of Heating,
Refrigerating and
Air-Conditioning
Engineers
HVAC
Heating,
ventilating, and
air-conditioning
PCO
Photocatalytic
oxidation
UV
Ultraviolet
UVGI
Ultraviolet
germicidal
irradiation
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
Irradiation
Will Air Cleaning Reduce Adverse Health Effects?
The ability to remove particles, including microorganisms, is not, in itself, an indication of the ability
of an air cleaning device to reduce adverse health effects from indoor pollutants. The use of air cleaning
devices may help to reduce levels of smaller airborne allergens or particles. However, air cleaners may not
reduce adverse health effects in sensitive population such as children, the elderly, and people with asthma
and allergies. For example, the evidence is weak that air cleaning devices are effective in reducing asthma
symptoms associated with small particles that remain in the air, such as those from some airborne cat
dander and dust mite allergens. Larger particles, which may contain allergens, settle rapidly before they
can be removed by filtration, so effective allergen control measures require washing sheets weekly, frequent
vacuuming of carpets and furniture, and dusting and cleaning of hard surfaces. (For more on allergen
control, visit www.epa.gov/asthma.) There are no studies to date linking gas-phase filtration, UVGI, and
PCO systems in homes to reduced health symptoms in sensitive populations.
10
Additional Factors to Consider
When making decisions about using air cleaning devices, consumers should also consider:
* Installation: In-duct air cleaning devices have certain installation requirements that must be met, such
as sufficient access for inspection during use, repairs, or maintenance.
* Major Costs: These include the initial purchase, maintenance (such as cleaning or replacing filters and
parts), and operation (such as electricity).
* Odors: Air cleaning devices designed for particle removal are incapable of controlling gases and some
odors. The odor and many of the carcinogenic gas-phase pollutants from tobacco smoke will still
remain.
> Soiling of Walls and Other Surfaces: Ion generators generally are not designed to remove the charged
particles that they generate from the air. These particles may deposit on room surfaces, soiling walls
and other surfaces.
* Noise: Noise may be a problem with portable air cleaners containing a fan. Portable air cleaners
without a fan are typically much less effective than units with a fan.
www.epa.gov/iaq
-------
Guide to Air Cleaners in the Home
Conclusion
Indoor air pollution is among the top five environmental health risks. 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 may,
however, 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 to control the levels of airborne
allergens, particles, or, in some cases, gaseous pollutants in a home, they may not decrease adverse health effects from
indoor air pollutants.
Additional Information
More in-depth analysis of air cleaners is available in the EPA technical document Residential Air Cleaners:
A Summary of Available Information (Second Edition), EPA402-F-07-043, October 2007-
Web site: www.epa.gov/iaq/pubs/residair.html
An electronic copy of this brochure, EPA 402-F-07-018, is available at www.epa.gov/iaq/pdfs/aircleaners.pdf
For additional hard copies of this brochure and other EPA indoor air publications, contact:
National Service Center for Environmental Publications (NSCEP)
PO. Box 42419
Cincinnati, OH 42419
phone: (800) 490-9198
fax: (301) 604-3408
Web site: www.epa.gov/ncep
www.epa.gov/iaq
-------
Office of Air and Radiation EPA- 402-F-07-018
Indoor Environments Division October 2007
(6609J)
------- |