In tighter, more energy-efficient buildings, pollutants are not as readily removed by natural ventilation. Filters or electronic air cleaners trap particulate (tiny particles) from the air flowing through them and re-circulate the cleaned air back to the building interior.
In Forced-Air Systems:
Cleaners can be installed in central forced-air heating or cooling systems by heating or air conditioning contractors. Standard filters, of disposable fiberglass (commonly used in furnaces) or washable metal mesh cost the least but are the least efficient, trapping only large particles. It should be noted - fiberglass or mesh filters should be changed every 30 days, for maximum system efficiency. Media filters contain a medium, such as cellulose, activated charcoal, etc. which traps smaller particles and which must be replaced at least annually. A medium such as charcoal will remove odors from the air
Electronic air cleaners are by far the most efficient cleaners of indoor air and the most expensive. They attract and retain pollutants like a powerful magnet. Millions of airborne dust, smoke, and pollen particles are carried through return air ducts to the electronic air cleaner. When they reach the unit, the larger particles are trapped by a screen pre-filter. Smaller particles pass through to the ionizing section where they receive an electrical charge. These charged particles continue through the cell to the collecting area where they are attracted to a series of grounded plates. The pollutants are held in this section until washed away during cleaning. Electronic air cleaners are 10 to 20 times more efficient than standard filters.
Portable Air Cleaners:
These also operate with a filter, standard or media type, or are electronic air cleaners. Some will clean air in only one room; others are large enough to clean air in two or more rooms. An electronic cleaner produces negative ions that are attracted to the pollutants. All units with claims saying that they clean the air electronically may not have a negative-ion generator. Units that have a negative-ion generator may produce some ozone.
The units operate in one of two ways. In the first type, negative ions are expelled to room air where the ions attach themselves to pollutants that become negatively charged and are attracted to the nearest positive surface. These deposited pollutants must be removed from surfaces in the room. In the second type, air is drawn through a pre-filter in the unit that removes larger particles of pollen and dust and traps some tobacco smoke and odors. The generator in the unit produces negative ions that attach to small particles of dust, smoke and other pollutants as the air passes through the cleaner. The charged particles are then attracted to a positively charged plate before the air is returned to the room. A fan is needed to pull air through the charging area and to return the cleaned air to the room. The pre-filter and the plate collector must be cleaned periodically by washing, or be replaced.
Consumers considering the purchase of an air cleaner/freshener should determine type of air cleaning needed to provide the desired air quality. If odor and larger particle removal would result in satisfactory air quality, the filtering system cleaner may be adequate. If fine particles that may cause allergic reactions must be removed an electronic unit may be needed at a higher price.
Cleaning Air Cleaners:
For any air filter to work efficiently, it must be cleaned or replaced regularly. Dirty filters add up to more money for the consumer because they force the heating/cooling system to circulate the air while pulling it through a clogged and dirty filter.