United States
Environmental Protection
                                                           Air and
                                February 1991
Indoor Air Facts
Use  and  Care  of
Home  Humidifiers
   Research and
No.  8
                                   lumidifiers 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 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 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.
                                                                       Printed on Recycled Paper

    [onsole 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

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
 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.
B  Steam vaporizer, which create
steam by heating water with an
electrical heating element or
electrodes. "Warm mist" humidifi-
ers are a type of steam vaporizer
humidifier in which the steam is
cooled before editing the machine.

Note:  Steam vaporizer and evapora-
tive humidifiers ajre 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 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

     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:
           Use 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, deionization
                   and reverse osmosis, remove most of me 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.
                        Consider using demineralization cartridges,
                        cassettes, or filters if supplied or recommended
                        for use with your humidiffier.
                   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.

    jt is important to use a humidifier
only whertconditions require it, to
use the correct moisture setting for
existing conditions, and to clean it

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

 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 present 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

 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, 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 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

  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

For additional EPA publications on indoor air quality, contact:

Indoor Air Quality Information
P.O. Box 37133
Washington, DC 20013-7133
For additional information on home humidifiers and
other consumer products, contact:

U.S. Consumer Product Safety Commission
Washington, DC 20207