United States	Air and	Research and
Environmental Protection	Radiation	Development
Agency	(ANR-445-W)	(MD-56)
&EPA
February 1991	
Indoor Air Facts No. 8
Use and Care of
Home Humidifiers
INTRODUCTION
lilumidifiers are commonly used
in homes to relieve the physical
discomforts of dry nose, throat, lips,
and skin. The moisture they add to
dry air also helps alleviate common
nuisances brought on by winter
heating, such as static electricity,
peeling wallpaper, and cracks in
paint and furniture. However,
excess moisture can encourage the
growth of biological organisms in
the home. These organisms include
dust mites, which are microscopic
animals that produce materials
causing allergic reactions to house-
hold dust, and molds.
"Recent studies by the Environmental
Protection Agency (EPA) and the
Consumer Product Safety Commis-
sion (CPSC) have shown that
ultrasonic and impeller (or "cool
mist") humidifiers can disperse
materials, such as microorganisms
and minerals, from their water tanks
into indoor air. At present, only
limited information is available on
the growth of microorganisms and
the dispersal of microorganisms and
minerals by home humidifiers.
Proper care and cleaning of ultrasonic
and impeller humidifiers are impor-
tant for reducing potential exposures
to microorganisms, such as bacteria
and molds. Microorganisms often
grow in humidifiers which are
equipped with tanks containing
standing water. Breathing mist
containing these pollutants has been
implicated as causing a certain t\pe
of inflammation of the lungs.
The Federal government has not
concluded that the dispersal of
minerals by home humidifiers poses a
serious health risk. Nevertheless,
using water with lower mineral
content will reduce exposures to these
materials (see box on the next page >
The young, the elderly, and those
people with lung diseases or respira-
tory allergies may be particularly
susceptible to certain types of air-
borne pollutants. However, if you
follow the recommendations for the
use and care of home humidifiers
provided in this fact sheet, the
potential for dispersal of microorgan-
isms and minerals from your humidi-
fier should be reduced.

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TYPES OF HUMIDIFIERS AND ASSOCIATED POLLUTANTS
IQonsole humidifiers are encased
in cabinets which are designed tor
floor use. Portable humidifiers are
smaller and more readily moved.
Central humidifiers are built into
heating and air-conditioning
systems, and humidify the whole
house.
The two types of humidifiers which
generally appear to produce the
greatest dispersions of both micro-
organisms and minerals are:
¦ Ultrasonic, which create a cool
mist by means of ultrasonic sound
vibrations.
¦	Impeller, or "cool mist," which
produce a cool mist by means
of a high speed rotating disk.
Two additional types of humidifiers
can allow for growth of micro-
organisms if they are equipped with
a tank that holds standing water, but
generally disperse less, if any. of
these pollutants into the air.
These are:
¦	Evaporative, which transmit
moisture into the air invisibly by
using a fan to blow air through a
moistened absorbent material,
such as a belt. wick, or filter.
¦ Steam vaporizer, which create
steam by heating water uith an
electrical heating element or
electrodes. "Warm mist" humiditi-
ers are a type of steam vaporizer
humidifier in which the >team is
cooled before exiting the machine
Note: Steam vaporizer and e'. opera-
tive humidifiers are not expected to
disperse substantial amounts or
minerals. A steam vaporizer te>ted b>
EPA did not disperse measurable
amounts of minerals: evaporative
humidifiers have not been tested bv
EPA for mineral dispersal.
Can I Use Tap Water in My Ultrasonic or Impeller Humidifier?
The Federal government has not concluded that using
tap water in ultrasonic or impeller humidifiers poses a
serious health risk. However, researchers have docu-
mented that these humidifiers are very efficient at
dispersing minerals in tap water into the air. In
addition, some consumers are bothered by a "white
dust" that may appear on surfaces during use of these
devices. Most importantly, minerals in tap water may
increase the development of crusty deposits, or scale, in
humidifiers. Scale can be a breeding ground for
microorganisms.
Retarding the growth of scale is the most compelling
reason to find alternatives to tap water. For this reason,
or if white dust is a problem or you wish to minimize
your exposure to minerals in the tap water as a matter
of prudence, you should either:
U Um bottled water labelled "distilled"
While distilled water still contains some mineral
content, it will likely contain lower mineral content
than most tap water. Distillation is the most effective
method for removing minerals from water.
Two additional demineralization processes, deiomzation
and reverse osmosis, remove most of the minerals from
water, but are generally less effective than distillation
Water demineralized by these two processes would, on the
average, be expected to contain a higher mineral content
than distilled waters. "Purified" water may be produced
by any of these three or other similar processes.
Be aware, however, that not all bottled water is produced
using demineralization processes. Bottled waters labelled
"spring", "artesian" or "mineral" have
not been treated to remove mineral content.
mm Consider using demineralization cartridges,
cassettes, or filters if supplied or recommended
for use with your humldifner.
Be aware, however, that the ability of these devices to
remove minerals may vary widely. Further research i*
needed to determine how well, and how long, these
devices work. Watch for the appearance of "white duM.
which would indicate that minerals are not being removed
Also, in areas of the country where the mineral content 
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RECOMMENDATIONS FOR USE AND CARE
^]t is important to use a humidifier
only when conditions require it. to
use the correct moisture setting for
existing conditions, and to clean it
thoroughly.
The possible health effects resulting
from the dispersal of microorganisms
and minerals by home humidifiers
are not fully understood. Mean-
while. it may be prudent to reduce
the potential for personal exposures
to these materials by taking the
following precautions, particularly
when using ultrasonic and impeller
humidifiers.
Empty the tank, wipe all surfaces
dry, and refill the water in portable
humidifiers daily to reduce any
growth of microorganisms; follow
the manufacturer's instructions
for changing water in console
humidifiers. Be sure you unplug the
unit from the electrical socket first.
Use water with low mineral content
to prevent the build-up of scale and
the dispersal of minerals into the air.
See the box on the left for informa-
tion on using water with low mineral
content.
¦ Clean portable humidifiers every
third day. Empty the tank and use a
brush or other scrubber to clean it.
Remove any scale, deposits, or film
that has formed on the sides of the
tank or on interior surfaces, and wipe
all surfaces dry. Again, be sure you
unplug the unit.
Follow the manufacturer's sugges-
tions on the use of cleaning products
or disinfectants. In the absence of
specific recommendations, clean all
surfaces coming in contact with
water with a 3% solution of hydro-
gen peroxide. If you use any
cleaning or disinfecting agent, rinse
the tank thoroughly with several
changes of tap water to prevent
dispersal of chemicals into the air
during use.
¦	Follow the manufacturer's direc-
tions on cleaning and maintaining
console and central (furnace-
mounted) humidifiers. In particular,
if the humidifier contains a tank, do
not allow water to stand in the tank
for extended periods of time, and
keep the water clean.
¦	Keep steam vaporizer humidifiers
out of the reach of children. Steam
and boiling water may cause burns.
¦	Do not humidify to indoor relative
humidity levels exceeding 50 percent
Higher humidity levels may encour-
age the growth of biological organ-
isms in the home. Hygrometers,
available at local hardware stores,
may be used to measure humidity
levels. Some humidifiers contain a
built-in humidistat which may be
adjusted to the proper moisture
level. If water condenses on win-
dows. walls, or pictures, either
relocate the humidifier, lower its
humidistat setting, or reduce its use.
¦	Do not permit the area around the
humidifier to become damp or wet.
If dampness occurs, tum the output
volume of the humidifier down. It'
the humidifier output volume
cannot be turned down, use the
humidifier intermittently. Do not
allow absorbent materials. >uch
carpeting, drapes, or table cloths, to
become damp.
¦	Follow the manufacturer's
instructions regarding the use,
maintenance, and replacement of
any materials supplied with the
humidifier. Use appropriate materi-
als as recommended by the product
manufacturer.
¦	Clean the humidifier, as directed,
at the end of the humidifying season
or when the product will not be in
frequent use. Before storage, make
sure all the parts are dry. Dispose
of all used demineralization car-
tridges. cassettes, or filters. Store
the unit in a dry location. After
storage, clean the unit again and
remove any dust on the outside.
¦	Stop using your humidifier and
contact your physician if you have
respiratory symptoms which you
believe are associated with periods
of use of your home humidifier, even
if you are following maintenance
directions.
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ADDITIONAL SOURCES OF INFORMATION
For additional EPA publications on indoor air quality, contact:
Public Information Center
U.S. Environmental Protection Agency
Mail Code PM-21 IB
401 M Street. SW
Washington. DC 20460
For additional information on home humidifiers and
other consumer products, contact:
U.S. Consumer Product Safety Commission
Washington, DC 20207
United States
Environmental Protection
Agency
Official Business
Penalty for Private Use $300
Office of Air and Radiation
Indoor Air Division (ANR-445-W)
Washington, DC 20460
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