Blueair 650E

The Blueair 650E delivers a prodigious amount of clean air per minute on its high speed (although reviews say that it's noisy), and it's extremely quiet on low speed. It also has sensors to read the level of pollution in the air and adjust its cleaning accordingly. This air purifier doesn't use a true HEPA filter, but reviews say its proprietary technology (a combination of a HEPA-like filter with ionization) appears to work just as well: It does an outstanding job clearing the air of dust, pollen and cigarette smoke in one reputable test. On the downside, replacement filters are relatively expensive (*Est. $80) and should be changed every six months, whereas true HEPA filters usually last a year or more. The Blueair 650E also lacks the prefilter that top-rated purifiers in this price range use to extend the life of the expensive main filter. It does offer an optional carbon SmokeStop filter (*Est. $150) to capture smoke and odors.

Experts warn that air purifiers using ionizers usually emit at least some ozone, a lung irritant than can exacerbate asthma. Although the Blueair 650E's ozone emissions have been independently tested and certified to be below 50 parts per billion, the upper limit set by the U.S. Food and Drug Administration for medical devices, experts including ConsumerReports.org recommend avoiding any air purifier that emits even small amounts of ozone. The competing Austin Austin Air HealthMate (*Est. $490) costs less than the Blueair 650E and can last up to five years on one filter, although it lacks the Blueair 650E's automated pollution sensors. Still, the Austin Air purifier emits no ozone.

ConsumerReports.org conducts the most detailed testing of the Blueair 650E, measuring its air-filtering performance and noise level and comparing it with 21 other portable air cleaners. The Blueair 650E air purifier is also evaluated in-depth by experts at the enthusiast site Air-Purifier-Power.com and the retail site AllergyBuyersClub.com, both of which find similar benefits and drawbacks to this model. The Association of Home Appliance Manufacturers has independently verified Blueair's clean-air delivery and ozone claims. The review at AchooAllergy.com is cursory, but it does identify Blueair as the one of the quietest air cleaners you can buy.