Breathe Easy: Indoor Air Filters For Your Home

Enlarge Image Image Gallery 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.