United States
Environmental Protection
Agency
Air and Radiation (6609J)
Research and Development
(MD-56)
February 1991
Indoor Air Facts No. 8
Use and Care of
Home Humidifiers
Introduction
Humidifiers 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 household dust, and molds.
Recent studies by the Environmental Protection
Agency (EPA) and the Consumer Product Safety
Commission (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 important 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 type 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 respiratory allergies may be particularly
susceptible to certain types of airborne 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
microorganisms and minerals from your humidifier
should be reduced.
Types of Humidifiers and Associated Pollutants
Console humidifiers are encased in cabinets
which are designed for 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
microorganisms and minerals are:
• Ultrasonic, which create a cool mist by means
of ultrasonic sound vibrations.
• Impeller, or "cool mist," which produces a
cool mist by means of a high-speed rotating
disk.
Two additional types of humidifiers can allow for
growth of microorganisms 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.
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Steam vaporizer, which create steam by
heating water with an electrical heating element
or electrodes. "Warm mist" humidifiers are a
type of steam vaporizer humidifier in which the
steam is cooled before exiting the machine.
Note: Steam vaporizer and evaporative humidifiers
are not expected to disperse substantial amounts of
minerals. A steam vaporizer tested by EPA did not
disperse measurable amounts of minerals;
evaporative humidifiers have not been tested by
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 documented 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:
1. Use bottled water labeled "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,
deionization 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 labeled "spring",
"artesian" or "mineral" have not been treated
to remove mineral content.
2. Consider using demineralization cartridges,
cassettes, or filters if supplied or
recommended for use with your humidifier.
Be aware, however, that the ability of these
devices to remove minerals may vary widely.
Further research is needed to determine how
well, and how long, these devices work.
Watch for the appearance of "white dust,"
which would indicate that minerals are not
being removed.
Also, in areas of the country where the
mineral content in the tap water is high, using
distilled water may be less expensive than
cartridges, cassettes, or filters.
Recommendations for Use and Care
It 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. Meanwhile, 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 information on using water
with low mineral content.
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• 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 suggestions 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 hydrogen 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 directions 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 encourage the growth of biological
organisms 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 windows, walls, or pictures,
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,
turn the output volume of the humidifier down. If
the humidifier output volume cannot be turned
down, use the, humidifier intermittently. Do not
allow absorbent materials, such as carpeting,
drapes, or tablecloths, to become damp.
• Follow the manufacturer's instructions
regarding the use, maintenance, and
replacement of any materials supplied with
the humidifier. Use appropriate materials 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 cartridges,
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.
Additional Sources of Information
For additional information on home humidifiers and
other consumer products, contact:
U.S. Consumer Product Safety Commission
Washington, DC 20207
www.cpsc.gov
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