Air Filtration and Purification

Every cubic foot of air in the average home is loaded with about three million dust particles. Most of these particles are so small they're not visible, but they can still be a health hazard, particularly for people who suffer from allergies and bronchial problems.

Air cleaners and purifiers can filter the air your household breathes noxious odors and gasses are often best eliminated by ventilation, but dust, dander, spores, smoke, and other particulates are most effectively removed with an air cleaner.

Air cleaning devices are either central filtration (often called "in-duct") systems put into the heating, ventilation, and air conditioning (HVAC) system of a home or portable units with an attached fan to assist in reducing indoor air pollutants. Portable units include table top and room size models.

Central Filtration System vs. Portable Devices

Whether to choose a whole-house or self-contained model depends on the type of heating system in your home. If you have a forced-air system, you should buy a unit that attaches to it since the effectiveness of a portable model will quickly be defeated by the system's circulation of unfiltered air throughout the house. Generally, portable units are used when air cleaning is desired in a single room.

Whole-house units work silently, efficiently and clean a great deal of air -- about 1000 CFM. These systems require professional installation and work only when the central heating or air conditioning fan is running.

With a tabletop or room air cleaner, pay attention to how many CFM (cubic feet per minute) of air move through the unit. For each 250 square feet of space, figure you'll need about 100 CFM. Room models can handle up to about 400 CFM, and tabletop models top out at about 175 CFM. 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.

The best types of filters are called ULPA and HEPA filters. If the unit contains one of these filters, find out how big it is. Obviously, a 12-by-16-by-6-inch filter will be much more effective (and costly) than an 8-by-8-by-6-inch filter.

Generally, the more filtration devices - the better. Air passes first through a pre-filter, trapping larger particles, then through additional filters like a Hepa, or carbon filters. Certified Hepa filters can remove more than 98%% of particles that are airborne making these the most efficient. Each filter stage means more screening and removal, so more is better.