Breathe Easy: Indoor Air Filters For Your Home

Capture and remove air pollutants from your home with an indoor air filter.

| July/August 2009

  • The Steril-Zone portable room air filter from Steril-Aire cleans air without producing ozone.
    Photo Courtesy Steril-Aire

The air you breathe inside your home can be more polluted than the air outside—even in the most smog-filled cities. The Environmental Protection Agency (EPA) estimates that, in many cases, indoor pollutant levels are two to five times higher than outdoor levels.

So what can you do? The first step is to eliminate as many pollutant sources as possible. The second step is to capture what’s left by actively removing it (vacuuming and cleaning) or filtering it. The most common location for a filter is in the return ductwork of a heating, ventilating and air-conditioning (HVAC) system that services the entire house. You can use portable room air cleaners for single rooms.

Mechanical air filters range from inexpensive, disposable models to hospital-grade HEPA (high-efficiency particulate air). Most mechanical filters display a Minimum Efficiency Reporting Value (MERV) ranging from 1 to 20, which indicates how well a particular filter captures micron-size particulates. The higher the MERV, the better the filter is at removing particles from the air.
Flat or panel filters usually are made with fiberglass, although some use natural materials such as animal hair or coconut fibers. The fiberglass filters are cheap, but have a MERV of only 1 to 4, so they’re mostly protecting your HVAC from clogs, not doing much to clean the air. Washable filters perform a little better and can last up to five years, but they require monthly cleaning.
Medium-efficient filters with a MERV of 5 to 13 are a practical choice for most homes. Typically made of a pleated material ranging from 1 to 6 inches thick, they achieve higher efficiency because they have more surface area for air to pass through. Some are made with fibers that have been electrostatically charged, working like magnets to capture tiny particles. However, they can lose some of their charge and become less efficient when they get dirty; nearly all filters drop in efficiency when particulates build up. 

Filters with the highest MERVs are best for people suffering from health issues such as allergies or asthma. The EPA reports that filters with a MERV of 14 to 16 can be nearly as efficient as HEPA filters (which have a MERV of 17 to 20 and are designed to remove at least 99.97 percent of the particulates that pass through their filters). True HEPAs are rarely installed in residential HVAC systems because they can dramatically decrease airflow and cause mechanical problems. You’re more likely to find them inside portable units designed to clean the air of just one room instead of the entire house.  

Another option is an electronic air cleaner (also called an electrostatic precipitator). These use electricity to create an electrostatic attraction that traps charged particles as small as .0001 microns onto a washable, reusable flat plate made of metal, glass or fiberglass. A Canada Mortgage and Housing Corporation study found electronic air cleaners to be the most efficient overall. On the downside, these cleaners generate ozone (20 parts per billion). As a comparison, the Food and Drug Administration (FDA) sets the ozone output of indoor medical devices to be no more than 0.05 ppb.

Don’t confuse an electrostatic precipitator with other air cleaners such as ionic air and ultraviolet germicidal irradiation (UVGI). Consumer Reports magazine found that a number of Sharper Image ionic purifiers failed to clean the air, and a class-action lawsuit alleging that the company misled consumers about its ionic air cleaners is said to have contributed to Sharper Image filing for bankruptcy.

A UVGI—which uses ultraviolet radiation from UV lamps to allegedly destroy biological hazards such as viruses, bacteria, allergens and molds—isn’t much better for your home. The Environmental Protection Agency is critical of the device, and says you’d need a higher UV exposure to have an impact.

No matter which filtering system you end up with, maintenance is key. Stay on top of cleaning and changing filters if you want to breathe easier—in all senses of those words.



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