Breathing Clean:
How Air Filters Provide Cleaner Living

Indoor air quality can be a problem

People spend up to 93% of their time indoors where - surprisingly - air pollution can be up to 10 times greater than outdoor levels. This poor indoor air quality results from reduced natural ventilation - a phenomenon that has developed in recent years from tighter, more energy efficient building construction. Indoor air consists of mostly invisible gases and particulates, including many which can be characterized as pollutants. These pollutants include many substances taken for granted, such as cooking smoke and grease, aerosol sprays, tobacco smoke, animal dander, ashes, human skin flakes, household cleansers, carbon dioxide, viruses, bacteria, pollen, and fungi. Fortunately, there is a way to have cleaner, fresher air, and that's by using air filters in your air conditioning and/or heating system. This pamphlet addresses particulates, non-pollutant gasses, which can have both short-term and long-term effects on life style and quality.

What air filters do

Air filters remove particulates before they soil furnishings, foul critical system components, cause discomfort, or otherwise spoil a comfortable indoor environment. As air is drawn to the central forced air system, it passes through the filter where particles of dirt and dust are trapped. The filtered, comfort conditioned air is then re-circulated back through the home. Consumers have a choice of three types of air filters: Standard filters, media filters, and electronic air cleaners. Each type differs in cleaning efficiency and costs. Portable air filters are also available for small area use. Some employ highly efficient HEPA (High Efficiency Particulate Air) filters which were previously used for specialized purposes, such as medical operating rooms. Your heating and air conditioning contractor or dealer can recommend which should be best for your home and your family's particular needs.

How much filtration do you need?

Standard filters such as the throw-away fiberglass and washable metal mesh filters are the least expensive of all air filters. They are designed to catch only the larger and more visible particles of dust and dirt that circulate through a forced air system. These filters should be checked every two months - and every 30 days during peak use of extensive indoor activity. Those filters that can't be removed and cleaned with water should be replaced. Disposable fiberglass filters are relatively inexpensive; most common sizes are available at hardware stores, drug stores, builder supply outlets, and convenience stores. Their efficiency is about 3 to 5 percent according to standard industry comparisons. (ASHRAE Standard 52.1-1992 "Gravimetric and Dust-Spot Procedures for Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter"). Media filters are more effective than standard filters, but also are more expensive. They can remove very small particles that require an optical microscope to be seen individually - such as pollen, lint, dust plant spores, cooking grease, and some tobacco and cooking smoke. The filtering material must be replaced at least annually - the homeowner removes the old material and discards it. The new filter material, available from heating and air conditioning contractors, is then positioned and inserted according to manufacturer's instructions. efficiency is about 25 to 35 percent. Electronic air cleaners, the most expensive of all air filters, also are the most efficient as shown on the following panels.

Electronic air cleaners remove up to 95% of dirt, dust, smoke

Electronic air cleaners are by far the most efficient cleaners of indoor air. Unlike standard or media air filters that merely get in the way of relatively large particles, electronic air cleaners attract and retain pollutants like a powerful magnet. Using electrostatic precipitation principles, they are even effective on particles so small that an electron microscope would be required to see them. While the larger particles of dirt are trapped by the screen pre-filter, the smaller microscopic particles (as small as one micron) pass through an ionizing section where they receive an electrical charge that traps them on the charged collector plates. Electronic air cleaners are 10 to 20 times more efficient than standard filters as they remove up to 95 percent of the dirt, dust, and smoke that otherwise circulate through the air. Electronic air cleaners also are energy efficient - most require no more power per day than a 40-watt light bulb. They feature permanent aluminum "cells" that can be rewashed in a dishwasher or laundry tub and reused almost indefinitely. Electronic air cleaners are available from air conditioning and heating contractors; builders can install them in new homes or remodeling projects.

Electronic air cleaners give particles a charge

Unlike standard or media air filters that merely get in the way of relatively large particles, electronic air cleaners attract and retain pollutants like a powerful magnet. Millions of airborne dust, smoke, and pollen particles are carried through the 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.

Particles caught by three air filters: standard, media, electronic

Electronic air cleaners effectively capture a wide spectrum of minute airborne pollution particles measured in microns (one 25,400th of an inch). Air cleaning efficiency varies with particle size. The efficiency of residential standard filters decreases rapidly on particles below 100 microns, and they are virtually ineffective on particles below 10 microns. Media air filters are 5 to 10 times more efficient than a standard filter, virtually 100% effective on particles above 10 microns, and effectively remove most dirty air particles down to 0.5 micron. Highest efficiency is achieved with electronic air cleaning, which effectively removes particles down to 0.01 micron, so small an electron microscope is required to see them.

Clean filters and other money savers

Keep filter clean. For any filter to work efficiently, it must be cleaned or replaced from time to time. Dirty filters add up to more money for the consumer because they force the heating/cooling system to circulate air while pulling it through a clogged and dirty filter. As previously explained, most filters can be easily inspected and cleaned or replaced by homeowners. Let contractors help. Air conditioning contractors also will check filters as part of preventive maintenance that is well worth its cost. This includes checking worn parts, such as belts and electrical contacts; making sure that the thermostat is working properly; and replacing or adding refrigerant if needed. Adjust thermostat properly. Another method of increasing efficiency includes installing thermostats which automatically raise and lower home temperature for prescribed periods to save energy. This also can be done with conventional thermostats. However, when you want to achieve rapid temperature change for comfort, don't set the thermostat higher or lower than the desired temperature. That doesn't cool or heat the home any faster - it just makes the system work longer. Keep doors and windows shut. Whenever a cooling or heating system is working, doors and windows should be shut - the system can't be helped by making it easier for outside air to flow into the house. When the freshness of outside air is wanted, turn off the air conditioning or heating unit first. Manufacturers of residential air conditioning and heating systems want consumers to know everything they can about achieving maximum comfort and efficiency while saving energy and money, too. If you have questions about your present system or how to improve it, call in an expert - a local air conditioning contractor such as those listed in the Yellow Pages of your telephone directory.

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