Air purifier misconceptions

The science of air cleaning can be confusing. Furthermore, the way some manufacturers present information can be misleading. The truth is, unless you're an excellent mathematician, it's difficult to determine which air cleaner is right for your specific needs, because you must weigh initial costs, frequency and cost of maintenance, power requirements, level and sources of pollution, room size and unit efficiency. On top of all this, there's no mandate from any independent scientific source that says what works best.

Four basic types of air purifiers

There are four main types of console-type air purifiers on the market. Many air cleaners use combinations of techniques.

HEPA air purifiers: These air cleaners use pleated high-efficiency particulate arresting (HEPA) filters to trap particles, along with a fan to pull air through the filter. By a wide margin, reviewers say this type of air purifier is the most effective. These models don't produce any ozone. Because they use fans, they can be noisy, but some are quieter than others.

Electronic ionizers: This type of air cleaner uses an electronic process to reverse the charge of particles in the air. The charged particles are then attracted to collection plates in the air purifier, as well as to objects in the room -- such as clothing, walls, floors and furniture. In effect, particles are removed from the air and deposited on your furnishings and clothing. You need to dust and vacuum to actually remove allergens from the room and prevent them from being reintroduced into the air. The Blueair 650E (*Est. $765) and Blueair 603 (*Est. $670) use ionizers, but they also use powerful fans and particulate filters. Electrostatic air purifiers produce a small amount of ozone, a lung irritant -- the main reason why experts do not recommend them.

UV purifiers: These devices rely on ultraviolet light to neutralize biological contaminants. Experts agree that UV light is effective in destroying microbes such as bacteria, dust mites and mold spores, given sufficient exposure time. According to the Federal Trade Commission, however, most home air purifiers fall short: "Bacterial spores would require a relatively long time under the light for the light to have a killing effect. Most household air cleaners move air too quickly to provide adequate exposure time." Without the addition of a filter and fan, UV purifiers are ineffective against particles such as dust, pollen and pet dander.

Ozone generators: Some air purifiers do nothing but produce large amounts of ozone. These units do not remove allergens from the air because ozone alone has no effect on particulate allergens. Ozone in large amounts can neutralize strong odors (such as the smoke odor from fire damage), but according to the U.S. Environmental Protection Agency (EPA), this is dangerous for human health, because ozone can cause lung damage, worsen asthma and cause other lung problems. The U.S. Food and Drug Administration (FDA) sets limits for ozone produced by medical devices, but these air purifiers don't claim to be medical devices. These types of air purifiers have been banned by California's Air Resources Board. This regulation is the first of its kind in the United States.

With all that in mind, reviews say to look for the following in an air cleaner:

  • The clean air delivery rate (CADR) should match the size of the room to be cleaned. CADR is a standard developed by the independent Association of Home Appliance Manufacturers (AHAM) to measure the removal of dust, smoke and pollen from the air. CADR measures the amount of clean air (in cubic feet) that an air cleaner delivers to a room per minute. According to the AHAM, an air cleaner's CADR should always be at least two-thirds your room's square footage. For example, a CADR of 80 is appropriate for a room of 120 square feet (assuming eight-foot ceilings). However, not all manufacturers have submitted their models for CADR testing.
  • A high-efficiency particulate arresting (HEPA) filter is the best way to filter air of dust, pet dander, pollen and mold spores. Experts generally agree that true HEPA filters, which trap 99.97 percent of particles as small as 0.3 microns, are the most efficient pollutant removers on the market. Some filters advertise themselves as HEPA or "HEPA-type" filters, but unless the word "true" appears in front, they may be lower-grade filters that don't trap as many pollutants. Some HEPA purifiers use additional carbon filters to trap odors and smaller particles like those in chemical fumes.
  • Air purifiers with fans work better in tests. Without a fan, air is not pulled through the unit to either charge particles and/or filter them through collection media like a HEPA filter.
  • A filter monitor alerts you when filters need to be changed. Proper maintenance is crucial for air-filter effectiveness. Once filters become clogged with particles, they can actually turn into air polluters, churning contaminants back into circulation. Some monitors have visual or audio cues that prompt you to change the filter. This feature is not essential. Since most HEPA filters need to be changed about once a year, it's easy enough to mark the date on your calendar.
  • Choose a noise level you can accept. Look for models with different fan speeds, so you can control the noise level. However, according to Mercia Tapping, president of AllergyBuyersClub.com, "Vendors routinely overstate the effective cleaning area of a machine because the area is calibrated at the machine's high fan speed. Now, try to sleep with that fan on high -- it sounds like a train going through your bedroom." Air-Purifier-Power.com tests air purifiers' noise levels on various speeds and reports the results in decibels, making it easy to compare models.

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