Many experts, including those at ConsumerReports.org, say most people don't need an air purifier. Although home air cleaners can be effective against larger airborne particles such as pet dander, dust and smoke, all of those allergens can be better controlled at the source by removing elements in the home that produce dust and by not smoking indoors, as well as by regular vacuuming and dusting.
Because portable air cleaners can remove only airborne pollutants, they are not very effective against dust mites and their droppings (they're too heavy to be airborne for long), which are a significant allergen for many people. Most air cleaners also don't remove most viruses or gases like carbon monoxide and radon. That's because even high-efficiency particulate arresting (HEPA) filters are most effective on particles larger than 0.3 microns, such as molds, pollen, dust, plant spores, pet dander and the larger particles in cigarette smoke. However, some pricier HEPA air purifiers, including the top-rated IQAir HealthPro Plus (*Est. $900) and the Austin Air HealthMate (*Est. $490), add carbon filters that they say can remove much smaller particles.
Most reviews agree that people with severe allergies, asthma and bronchitis -- who need to control indoor air quality as much as possible -- may benefit from air purifiers, but only when used in conjunction with other allergen-control strategies such as ventilation and daily HEPA vacuuming. These reviews say there's little evidence that air purifiers are effective alone. The Asthma and Allergy Foundation of America takes this stance: "Air filters are worth considering, but not as a solution to your asthma or allergy problems by themselves É the most effective step is to eliminate the source of these allergens and irritants in the first place."
The U.S. Environmental Protection Agency (EPA) has an excellent online document titled, "Residential Air Cleaners (Second Edition): A Summary of Available Information" (see our Useful Links section for the link to this article). The EPA doesn't take a position for or against home air cleaners, but it states, "The use of air cleaners may help reduce levels of smaller airborne allergens or particles, but should not be expected to effectively reduce health symptoms." Both the EPA and American Lung Association recommend that air purifiers be used as a last resort after allergen source control and ventilation. ConsumerReports.org recommends that you first ban smoking in your house, don't burn wood fires or candles, keep pets out of bedrooms and replace carpets with hard flooring: "In fact, if you don't have allergies, asthma or other respiratory illnesses, you may not need an air cleaner at all."
Before you buy a $500 air purifier, you might make a $23 investment in a simple whole-house furnace filter. If you have forced-air heating or cooling, these filters simply replace your regular furnace filter. Filters such as the 3M Filtrete 2200 Elite Allergen Reduction Filter (*Est. $23) do an outstanding job trapping dust and pollen in one leading test, and they do a good job with smoke. Filters need to be replaced every three months. Furnace filters can reduce air flow as they become dirtier, but the Filtrete filters allow very good airflow overall in tests.