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Types of Air Purifiers and Filters

There are several basic types of air cleaners in the budget segment, including ionic air purifiers and HEPA air purifiers with high-efficiency particulate air filters.

HEPA Air Purifiers.

In appearance, HEPA filters resemble the lint screens used in clothes dryers except that they are made of small, tightly woven fibers (often glass) as opposed to metal or plastic. Cheap HEPA air purifiers, such as the Hunter 30057 and -, trap 99.97 percent of airborne particles -- think dust, pollen, mold spores, pet dander -- as small as 0.3 microns (one micron equals 1/25,400 of an inch).
A less effective filter is a stepped-down HEPA-type filter like the one found on the Holmes HAP242-UC, which the company claims captures 99 percent of airborne dust and pollen particles that are at least 2 microns in size. The EPA points out, however, that airborne particles often settle before being drawn into the air purifier, so you won't get rid of all airborne pollutants by relying solely on a HEPA air purifier.

When looking at HEPA air purifiers, note the number of times air flows through the filter each hour; the more passes, the more opportunity to catch pollutants. Experts set the ideal at six air exchanges an hour. Among the cheap HEPA air purifiers on our list, the Hunter 30057 claims up to six air exchanges an hour and the Whirlpool Whispure 450 falls a bit short at 4.8 pass-throughs an hour.

Carbon Filters.

Many HEPA air purifiers, including the Whirlpool Whispure 450 and the Hunter 30057, as well as the Winix PlasmaWave 5300 (starting at $171) and the Hunter 30090 (starting at $70), also incorporate a carbon pre-filter that helps absorb odors and trap some larger particles. If smoke and/or odors are the primary problem, a cheap air purifier with a carbon filter (sometimes referred to as a charcoal filter) is a good choice. It uses activated carbon to absorb the volatile chemicals in the offending gases but doesn't remove pollen, mold, or other allergens from the air. That's why a carbon filter is often paired with a HEPA filter. The HEPA-type filter on the Holmes HAP242-UC gets an odor-absorbing boost from baking soda.

Ionic Air Purifiers.

Ionic air purifiers, such as the Sharper Image Ionic Breeze 3.0 and Oreck XL Tabletop Professional, catch the contaminants on electrically charged plates or cells instead of filters. They send out negatively charged ions that attach to airborne particulates, which are then lured back to a positively charged collector plate. Experts note, however, that some of these particles may be recirculated and some wind up settling on other surfaces in the room (like furniture and walls) and leave stains. In addition, ionic air purifiers produce small amounts of ozone, a known lung irritant, but supposedly at levels that do not exceed current safety standards (and do nothing to cleanse the air). Some consumer reviews express confusion about the ozone issue and are wary of ionic air purifiers.

The Holmes HAP242-CU augments its HEPA-type filter with an optional ionizer, as does the Hunter 30057. And the Oreck XL Tabletop Professional relies on a proprietary ionizing technology called a Truman Cell.

Review continues below

UV Air Purifiers.

In these models, ultraviolet germicidal irradiation destroys bacterial microorganisms as they pass through UV rays. The dead organisms are then collected in a filter. The scope of cheap ultraviolet air purifiers is limited to removing germs, viruses, and bacteria from the air, and they have no effect on allergens, smoke, or odors. Many cheap ultraviolet air purifiers, such as the Germ Guardian LW-18 UV-C (starting at $71), are hand-held, so you can wave them like a wand over the area you wish to purify.

Ozone Generators and Other Technology.

The most controversial air purifiers convert air molecules into ozone that tackles odors. Although there is scientific concern about the loss of ozone in the upper atmosphere (think global warming), scientists are also concerned that ozone in the lower atmosphere may have harmful side effects. The EPA warns that ozone can seriously damage your lungs, and at the very least, exacerbate respiratory problems. Consequently, experts recommend only using ozone-generating air purifiers in unoccupied rooms where the stench is otherwise impossible to remove.

Another approach, incorporated into the AirFree Onix 3000, uses a ceramic core to kill off organisms like spores, fungus, viruses, and bacteria, at temperatures of 400 degrees Fahrenheit. The company has a patent on the core and claims it will reduce 70 percent to 90 percent of the organisms in the ambient air within 10 days.

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