Blueair 603

The Blueair 603 -- like its sibling, the Blueair 650E (*Est. $765) -- earns some nods from reviewers for its ability to filter pollen, dust and smoke from the air in a large room quickly and effectively. Its low speed is whisper-soft, but experts say it works much better on its (loud) high speed. The Blueair 603 lacks several of the 650E's convenience features -- it has no electronic pollution sensors (to automatically crank the fan higher when it senses pollutants in the air), no remote control and no on/off timer. The filter-change indicator simply counts down six months, unlike the 650E which counts actual days of use.

Both Blueair purifiers use ionizers, which usually emit at least some ozone. Ozone irritates lungs and can worsen asthma. Both models' ozone output has been independently certified below 50 parts per billion, which is the U.S. Food and Drug Administration's limit for medical devices. Still, ConsumerReports.org advises steering clear of air filters that emit any ozone. The top-rated Austin Air HealthMate (*Est. $490) costs less than the Blueair 603 and doesn't emit ozone. The Austin Air's HEPA filter also lasts up to five years, unlike the Blueair's filters (*Est. $80), which must be replaced every six months.

AllergyBuyersClub.com, a retail site, tests and reviews the Blueair 603 and compares it with the Blueair 650E. ConsumerReports.org tests the 650E, but its results also generally apply to the similar Blueair 603. The Association of Home Appliance Manufacturers has independently certified Blueair's clean-air delivery rates and ozone levels. The review at AchooAllergy.com is shallow, singling out Blueair purifiers for their quietness.