Also be sure the model you choose isn't too noisy or drafty in its output and consider one that has intake and output on opposite sides of the unit for best efficiency. Check replacement filter prices, life and availability and be sure filters are easy to access. If the unit contains a HEPA filter, find out how big it is. Obviously, a 12 by 16 by 6-inch filter will be much more effective (and expensive) than an 8 by 8 by 6-inch filter.

Prices for room air cleaner models run from about $180 to $1000, usually depending on the quality of the mechanics and filtration. Tabletop units cost from $60 to $180.

Whether to choose a whole-house, room or tabletop model depends on a number of factors. Whole-house units work silently, efficiently and clean a great deal of air -- about 1000 CFM (cubic feet per minute). On the downside, they're relatively expensive, require installation by a contractor, and unless you leave the fan on, they only move air when the furnace or air conditioner kicks on. Of course, you must have a forced-air heating system to even consider a whole-house air cleaner because this type of unit shares the system's blower and ductwork.

If you want to clean the air in a limited area, such as the bedroom of someone who has severe allergies, a portable, room-size model might be the better choice. These focus their energy usage and filter capacity on the task at hand, and they can be moved from room to room or house to house when necessary. Whichever type you pick, if you choose a quality product and maintain it properly, you're sure to see a marked improvement in the quality of your home's air.

-- Tips courtesy of HomeAdvisor.com