The Dirt on AIR FILTERS

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HOW EFFECTIVE ARE THEY?

No air cleaning system can remove all pollutants from indoor air. In addition, there are no uniform standards for comparing systems, although most filters are tested and given an ASHRAE (American Society of Heating, Refrigeration and Air-Conditioning Engineers) rating (see " Do They Work? " ). Portable filters are sometimes given a Clean Air Delivery Rate (CADR) by the Association of Home Appliance Manufacturers (ARAM). This refers to the rate at which air is moved through the filter, measured in cubic feet per minute. In both ratings, the higher the number, the better.

Under the right conditions, the better filters can effectively remove many household pollutants. In addition, air cleaners may also contain absorbents (charcoal) and/or reactive materials to remove cigarette smoke and odors. Ozone generators designed to eliminate odors and kill bacteria are becoming increasingly popular, but, curiously, ozone in sufficient quantities is itself a pollutant and can cause shortness of breath and chest pain if allowed to accumulate. It is also important to understand that air cleaners cannot remove pollutants such as dust, dander and pollen once they settle. Another important consideration is that whole-house air cleaners usually only work when the heater/air conditioner is on; therefore, you may not have air cleaning when the temperature is mild.

PORTABLE FILTERS VERSUS WHOLE HOUSE FILTERS

All filter materials come in either a portable or whole house system - if you don't have a forced-air heating system, you are limited to the portable kind. Portables are generally cheaper than whole-house units, costing $80 to $500 depending on the size of the room you're filtering. They can be focused in high-risk areas such as the bedroom or living room. Look for units that have a "high-efficiency particulate air (HEPA) filter" or an "ultra-low penetration air (ULPA) filter." These filters work well for removing dust and smoke. Brand names, which include Honeywell, Panasonic, Holmes, Hunter and Kenmore, are available from a large variety of retail stores.

Whole-house air cleaners, on the other hand, filter all of the air in your house (as long as the windows are closed) and they can vary in price from as little as $1 to as much as a $1,000 with installation. A good, pleated electrostatic filter that replaces the ordinary fiberglass filters standard in most central heating units can provide reasonably good filtration for a very small price, about $10 to $15 (these filters must be changed periodically). It's important to note that washable electrostatic filters may not work as well as replaceable ones. For the most effective cleaning of indoor pollutants, however, you will probably need to spend at least $400 for an electronic precipitator unit. Brand names include Honeywell, Research Products, 3M, Purolator, Precisionaire and American Air Filter. While consumers can easily install small filters, larger units generally require a heating contractor, which may add significantly to the cost.

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