Getting started

Before you buy an air purifier, try some simple, common-sense steps to reduce indoor air pollution. Begin by vacuuming often, banning smoking indoors, minimizing use of candles and wood fires, and using exhaust fans in kitchen, bath, and laundry areas. Test your home for radon gas, which can cause lung cancer (test kits cost about $15). Don't store chemicals, solvents, glues, or pesticides in your house. Minimize the risk of deadly carbon monoxide gas by properly maintaining heating equipment, wood stoves, fireplaces, chimneys, and vents--and by installing

carbon-monoxide alarms on all levels of your home. And don't idle your car, run fuel-burning power equipment, or light a barbecue grill in your garage, basement, or in confined spaces near your home.

on all levels of your home. And don't idle your car, run fuel-burning power equipment, or light a barbecue grill in your garage, basement, or in confined spaces near your home.

Air-purifier models with an electrostatic precipitator remove pollutant particles by charging them as they pass through and collecting them on an oppositely charged metal plate or filter. In the process, they produce some ozone as a byproduct. You'll also find dedicated ozone generators, which produce relatively large amounts of this gas by design. While ozone in the upper atmosphere protects us from the sun's ultraviolet rays, ground-level ozone is an irritant that can worsen asthma and compromise your ability to fight respiratory infections. We believe that air purifiers that emit even small amounts of ozone are a poor choice if someone in your household has pulmonary problems or allergy symptoms. We also suggest that you avoid dedicated ozone generators entirely, given their high ozone emissions.

If you still want one, use this air-purifier guide to choose. The Association of Home Appliance Manufacturers certifies most room models as part of a voluntary program that includes appropriate room size and maximum clean-air delivery rate (CADR), a measure of cleaning speed. We judge a CADR above 350 to be excellent and below 100 to be poor. Choose a model designed for an area larger than yours for better cleaning at a lower, quieter speed. Many whole-house filters list a minimum efficiency reporting value (MERV), developed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. The top performers in our tests typically had a MERV higher than 10.

Learn more ways to improve the air quality at your home.

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Types

There are two basic types of air purifiers. Room models, which are most heavily promoted, can be moved from room to room. Whole-house models are built into the ductwork of a forced-air heating or cooling system and, as their name implies, filter the air in the entire house.

These are the only option for a home that doesn't have forced-air heating or cooling. Room air purifiers cost much less than whole-house models. Most room air purifiers weigh from 10 to 20 pounds, have a handle, and stand on the floor or on a table, while heavier models might have wheels. Some room models use a high-efficiency particulate air (HEPA) filter, which can capture ultrafine particles. Most HEPA filters need to be replaced annually, an expense that might approach the cost of the air cleaner (A few air cleaners are now available with cleanable HEPA filters.) Room models that use either electronic precipitator or ionizer technology produce some ozone, a lung irritant. And they might soil the walls by depositing some pollutant particles on them.

These are a subcategory of room models. Unlike electrostatic precipitators, which tend to emit small amounts of ozone as a byproduct, these niche products produce large amounts of ozone by design. According to manufacturers, that is to reduce allergens such as dust, smoke, pollen, germs, and mold. Ozone is a serious health concern. We judged the

two ozone generators we tested Not Acceptable as air purifiers.

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This type is a reasonable choice if your home has forced-air heating. But built-ins can be expensive to buy, and they must be installed professionally in the ductwork of your heating system and most need to be wired into your home's electrical system. Most of the built-in air cleaners we tested did an excellent job of removing dust and smoke particles from the air. Some use a high-efficiency filter. Those that use an electronic precipitator produce some ozone, and they might soil the walls by depositing pollutant particles on them.

Whole-house air filters These inexpensive alternatives to a whole-house built-in unit replace the existing furnace filter in your forced-air heating or cooling system. You simply slip out the old filter and slide in the replacement. But those we tested worked much less effectively than the built-in whole-house models, especially in clearing smoke. Some are conventional fiberglass filters; others are charged and pleated models. The latter are not electrically powered, even when they have names like Electroclean, so they don't produce ozone. The filter must be replaced every one to three months.

Features

Whole-house air filters generally include a range of standard sizes, with some that adapt to fit different-size filter-box or return-air openings. Room air cleaners usually use a fan to pull air into the unit for filtration. But don't expect a wide array of bells and whistles. Here are the air purifier features to consider.

Most room air cleaners use a fan to suck in air. Those without a fan run more quietly, but the ones we tested worked poorly.

A clogged air cleaner works inefficiently. You should remove and wash an electronic precipitator's collector-plate assembly every month or so. (You can do it in the sink or tub or put it in a dishwasher.) In most room and whole-house models that use an electronic precipitator, and in whole-house models that use a HEPA filter with ionizing circuitry, an indicator light lets you know when it's time to replace or clean the filter.

In some room models, these raise or lower the fan speed automatically. But we were unimpressed with those we tested. They didn't kick in until pollutant levels were high, and then they shut off before the levels dropped sufficiently.