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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.

Air filters

Purpose. Air-filtration systems pull mold, pollen, dust mites, and other particulates out of household air.

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 growth.

Health benefits. Dehumidifiers are critical