One of the most efficient ways to clean up indoor air pollution in a house is with a special filter that was developed during the Manhattan Project and is now used to keep the air clean in Silicon Valley computer chip plants, hospitals and the Kennedy Space Center.
Called HEPA -- for High Efficiency Particulate Absolute -- the filter comes in portable units that can be moved from room to room. Larger models attach to central air conditioning or heating ducts and can clean a whole house.
Whichever way it is used, HEPA filters earn very high marks for removing minute particles of various indoor pollutants and dust from the air.
"HEPA is very efficient," says Kevin Teichman, program manager of infiltration, ventilation and indoor air quality at the Department of Energy. The average filter captures about 25 percent of particles, Teichman says, compared to the near-perfect 99-plus percent for HEPA filters.
What HEPA filters can't do, however, is extract substances like carbon monoxide, a by-product of combustion, from the atmosphere. "[Carbon Monoxide] will go right through the filter," Teichman says.
At least two companies -- Control Resource Systems, Inc., in Michigan City, Ind., and Enviracaire in Hagerstown, Md. -- now manufacture the HEPA filters for home use. Average cost is about $ 500 to $ 800. The home can be treated with either portable units -- the number needed depends on the size of the house -- or a larger unit hooked into the central heating system.
Preliminary results also suggest that HEPA filters may even be helpful in removing radon from the air, says Ron Marsh, president of Control Resource Systems. Testing is underway in Pennsylvania homes to confirm the results.
One of the beauties of HEPA filters is that they don't take much maintenance or other care. The filter only needs to be changed every three to five years, compared with three to six months for an activated charcoal filter.
Among the other kinds of devices available for cleaning home air are: Electrostatic precipitator air cleaners, which attach to central heating or air conditioning, give an electric charge to particles in the air. These charged particles are then attracted to a collecting plate. The advantage of electrostatic devices is that they don't interfere with air flow, the way some filters can, but the drawback is that the collecting plates must be cleaned every few months. Air-to-air heat exchangers (or heat-recovery ventilators) blow stale air out of the house and draw in fresh air. But unlike an open window, which does basically the same thing, the ventilators extract heat from the stale air and use it to warm the fresh air. The result is cleaner air with fewer energy costs. But at $ 500 to more than $ 1,000, the ventilators themselves are quite an investment. Filters that attach to the furnace or air conditioning systems can also do some cleaning. Their disadvantages are that they are not as efficient as some of the other devices and they must be changed frequently.