We worry much about the air pollution outside our homes. There are dust, smoke, gases and chemical odors to justify our concern. But these pollutants, and maybe even more (animal dander, mold, and pollen), may also be present in the air inside our homes. It is for these different kinds of pollutants that the various types of air purifiers were made. Some types of air purifiers are effective in eliminating certain kinds of pollutants. It is therefore important that you first determine which pollutants you want to get rid of before buying a unit.

An air purifier that uses an activated carbon filter is best for ridding your home of noxious odors, such as those that emanate from tobacco smoke, perfume, formaldehyde, and pesticides. Those units without any special media (such as activated carbon) won't work against gaseous pollutants.

In reducing cigarette smoke, an electronic air purifier is most effective. However, this unit may not eliminate the odor. Two different varieties - negative-ionizing cleaners and electrostatic cleaners - charge particles in the air so that they can be collected by a special filter. While these units can counteract the obnoxious effect of some odors, they are not known to be effective in removing odorless gases (example, carbon monoxide). Also understand that these types of electronic air purifier won't work in relieving your allergy to dust, pollen, or animal dander.

A mechanical filtration system works best in trapping large particles, such as mold, pollen, and dust. An example of this type of air purifier is the high-efficiency particulate (HEPA) air filter. HEPA air filters, however, are effective in filtering only airborne particles; they are not as effective in getting rid of allergens, most of which quickly settle on surfaces. A hybrid unit that uses more than one type of filtration system is ideal for eliminating dust, pollen, gases, and odors.

The air purifier that you choose should match the size of your room. In order to know how many cubic feet of air per minute it can clean, look for the clean air delivery rate (CADR). Unless used in small areas, tabletop air purifiers are relatively ineffective. You also have to understand that no air purifier is effective on its own; it would therefore help a lot if the sources of the different pollutants are controlled.

If not properly installed and maintained, electronic air purifiers and negative-ionizing cleaners may produce ozone, a known lung irritant. Further, negative-ionizing cleaners, particularly those that lack a collection system, may eventually produce a hideous black film on your furniture and walls. Likewise, most air purifiers that are designed to eliminate gases may in fact send the gases right back into the air over time.

If you have central air conditioning, you can have a mechanical or electronic filter installed in the ducts. This can be equally effective in filtering allergens from the air.