IQAir HealthPro

Experts praise the HEPA-filtering HealthPro for its large coverage area (1,000 square feet, but it will work better in smaller rooms) and efficiency at removing particles. They also say it's the best air purifier for people with severe allergies. However, a few owners and experts point out that this air purifier can be loud on its highest speed setting. It's also expensive -- although not as expensive as its sibling, the IQAir HealthPro Plus (*Est. $900), which comes with a gas-and-odor filter capable of capturing volatile organic compounds (VOCs) from the air. (You can add the gas-and-odor filter later to the regular HealthPro if you want.) For most people, an IQAir machine would be overkill, experts say. A less expensive alternative is the Austin Air HealthMate (*Est. $490), which works almost as well at filtering the most common household allergens, chemicals, odors and germs and costs hundreds less.

The IQAir HealthPro series has been evaluated by two of the best sources for air-purifier reviews: the enthusiast site Air-Purifier-Power.com and AllergyBuyersClub.com, a retailer that points out the pluses and minuses of the products it sells. The HealthPro is also reviewed by a handful of owners at Amazon.com.