Air Filters, Dehumidifiers, and Humidifiers
Here are some tips for understanding the air in your house and the air-quality appliances
that can change it.
Purpose. Air-filtration systems pull mold, pollen, dust mites, and other particulates out of
The best systems use HEPA (high-efficiency particulate absorption) filters that have
multiple pleats that trap tiny particles. This filter can be installed professionally in
the duct next to the furnace fan. They also are available as portable room units.
Another kind of unit, the electronic cleaner, is especially good at sweeping mold
and pollen particles from the air. They catch them on an electrically charged plate.
The type of air cleaner known as an ionizer makes electrically charged ions that bond to
particles in the air and causes them to cling to walls, ceilings, and drapes.
Filter systems improve air quality by removing pollutants. HEPA systems can be up
to 99.9% efficient in removing floating particles from the air. Compare this with
regular furnace filters. These are only 10% efficient in removing lint from the air.
For a filtration system to be fully effective, it needs to run 24 hours a day.
Health benefits. A good air-filtration system can make a difference for people with severe allergies
or asthma. It’s not as necessary for the average person. Keep in mind that studies
have not proved that any filters dramatically reduce allergy or asthma symptoms. The
best possible benefit may come from HEPA filters. So before you invest a lot of money,
make sure you take other steps first. In general, families with allergy problems should
first look for and eliminate or control the source of the problem like pets, rugs,
dust mites, and moldy areas in the home.
Disadvantages. Air-filtration systems need to be strictly maintained. Changing the filters according
to the manufacturers' instructions is key to the success of the system. Also, these
systems are no substitute for good indoor hygiene. If you have a cat, dog, or old
rugs, if your house is dusty, or if you leave your windows open, the filtration system
can't do its work well.
Some systems with smaller motors are noisy, especially for the bedroom. They don't
turn the air over as quickly and as well as larger units.
In the case of ionizers, the particulates that were sent clinging to your walls, ceilings,
and drapes fall off in a few days. Then they are back into your breathing environment.
It is important to note that some electronic filters like an ionizer can produce ozone.
Ozone is a lung irritant.
Purpose. Dehumidifiers remove moisture from the air. This curbs the growth of mold and dust
mites. They are particularly useful in parts of the house where humidity collects
like damp basements.
Dehumidifiers draw air over cold coils, condensing out its moisture, before passing
the air over warm coils and back into the room. (Air conditioners also take a certain
amount of moisture out of the air, but dehumidifiers do this much more efficiently.)
The condensed water drips into a container in the unit that has to be emptied. The
water can be directed to a drain by means of a hose.
Home dehumidifiers remove between 10 pints and 50 pints of water from the air each
day. The amount depends on the relative humidity. The capacity of a unit is measured
by the number of pints it can remove in a 24-hour period at 60% relative humidity
and at 80°F (27°C).
Harmful dust mites, those microscopic organisms that particularly make allergy and
asthma sufferers feel worse, thrive in high humidity. They live in your bedclothes,
your drapes, your rugs, and the air in your home. Removing excessive moisture from
indoor air helps control these pests. Dehumidifiers also can help limit mold and bacterial
Health benefits. Dehumidifiers are critical for households in humid climates with very old people
or very young children, or for families with a history of allergies or asthma. In
their first 2 years of life, children spend a lot of time on the floor or rug. If
you have a 10-year-old rug, it likely has a host of dust mites that thrive in the
high humidity. And the more you are exposed to something to which you have an inherited
leaning to be allergic, the more likely you are to become allergic to it. It could
be mold, bacteria, or dust mites.
Disadvantages. Mold can grow in the drainage areas of a dehumidifier. Regularly clean the water
basin with bleach. Also, smaller units may not dry out the air satisfactorily all
the time. You should consider choosing a larger capacity unit like one rated at 50
pints a day or more. It can always be turned down.
Purpose. Humidifiers are of great use during winter in cold climates where home heating systems
are in constant use. This dry air can dry out and irritate your eyes, throat, and
lungs. Dry skin is another problem. Besides that, you may find the wood in your house
drying out. This can create gaps between floorboards, loose furniture joints, and
windows that rattle in their frames.
Humidifiers come in 2 types:
The evaporator type forces air over water inside the unit and blows the evaporated
water into the house.
The atomizer type of humidifier breaks up water droplets and makes a mist that then
dries up as it is spread throughout the house. To break up water into a mist, some
of these humidifiers use a rotating device like a blade or brush. In the case of an
ultrasonic humidifier, a disc that moves back and forth at about 1.6 million times
per second does the job. The water is changed into fine droplets.
Humidifiers can be built in to your central heating system and use the furnace ducts
to spread moist air throughout your home. If you have a closed heating system like
electric baseboards, a central humidifier can be installed with its own fan and duct
for spreading the humidified air.
Portable humidifiers vary in size and efficiency. Tabletop units can usually handle
only single rooms. Larger console models can be set up in central locations to spread
moisture to a large area of the house.
Health benefits. Humidifiers are recommended for people who live in areas where houses must be heated
for a good portion of the year. They are also recommended for those who live in very
dry climates. Humidifiers may help those suffering from sore throats, headaches, nosebleeds,
and coughs related to dry air. In general, a moist house is more comfortable than
a dry one.
Disadvantages. Humidifiers are not easy to use. All units, portable as well as those installed in
central heating systems, must be cleaned thoroughly. Otherwise, they tend to become
contaminated with mold and bacterial growth that may be blown through the house. Stop
the humidifier and call your health care provider if you develop any respiratory symptoms
that you feel are related to the use of a humidifier.
Clean portable and central units according to manufacturers' instructions.
Ultrasound humidifiers tend to leave a fine white dust about your rooms. The tiny
droplets they give out evaporate and leave behind calcium carbonate and other minerals
present in the water. Use distilled (not de-ionized) water in the humidifier to prevent
this. Distilled water, however, is fairly expensive.
Aim for the right amounts of humidity:
The air in your home should range from 30% to 55% humidity.
If the humidity is too high, mold and dust mites may thrive. Both are common causes
of allergies. Mold also causes an unpleasant smell and can discolor surfaces.
If the humidity falls too low, the people in your home may suffer dry eyes and may
develop throat and sinus irritations. The simplest way to measure humidity is with
a gauge called a humidistat. These gauges are often packaged with thermometers. You
can usually buy one in a hardware store for less than $10.