Furnace filters protect the furnace. They also contribute to good health and well-being by cleaning the air circulating through the house. Filter designs and rating systems vary. Some filters remove large, heavy particles from the air but allow smaller particles to flow through. Large particles (from 6 to 100 microns in size) include lint, pollen, and mold spores. Medium particles (from 0.3 to 6 microns) include dust, animal dander, and bacteria. The smallest particles (0.3 microns and below) include smoke, smog, and viruses. By comparison, a human hair is between 3 to 200 microns.
The American Society of Heating, Refrigeration, and Air Conditioning Engineers has devised a rating system for filters. They use numerical values ranging from 1 to 12, with the higher number capturing more of the dust.
The 3M Company, a major manufacturer of filters, primarily uses a Filter Performance Rating (FPR). It is based on the ability of the filter to capture particles from 0.3 to 1.0 microns. These sub-micron particles are most likely to be inhaled, where they can cause problems in the lungs. Their rating of filters range from 300 to 1600.
The effectiveness of various filter types in removing sub-micron particles is:
Air filters capture many of the allergens that aggravate allergy and asthma symptoms. Pollen, molds, and dust are common in any household and can be reduced by using a furnace filter.
The filter will also keep your heating or air conditioning system coils cleaner, which can save up to 15 percent on your energy bills.
A general guideline is to change filters at least every three months to maintain maximum efficiency. Some types of filters, however, may need to be washed or replaced more often, so check monthly. Change furnace filters according to the manufacturer's directions, and use the filter they recommend.
The following factors affect the life of a filter:
Read the manufacturer's instruction manual for recommended care.
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