Part of a forced-hot-air system, a furnace includes a heating source, blower motor, air filter(s), ducts to send heated air throughout the home, and return-air ducts for sending relatively cooler air back to the furnace.
The furnace filter is the most important component homeowners can maintain easily. Without a filter, dust will get blown all over the house, thwarting your cleaning efforts and reducing the indoor air quality. A neglected filter will clog with dust and debris, restricting the air flow and adversely affecting the unit’s energy efficiency. Furnace filters in households with multiple pets can also experience clogging from pet hair.
A wide range of air filters are available: fiber-and-paper filters; those made of polyester or fiberglass; HEPA (high efficiency particulate air) filters, for those with allergies or dust sensitivities; and even “permanent” filters that can be washed and returned to service.
Single-use filters should be check or replaced regularly during the heating season. Wash permanent filters by spraying an all-purpose household cleaning liquid on both sides of the filter, letting the cleaner work for several minutes, then rinsing the filter thoroughly from both sides. Dry the filter completely before re-installing. If you live in a very cold climate and choose a permanent filter, buy two for alternating service: Take the dirty filter out, install the clean filter and clean the dirty one right away. That way, you won’t have to shut off the heat while the filter dries.
Even if you buy good filters and replace or clean them regularly, some dust and dirt will sneak past and accumulate in the ductwork. Studies are under way to find out whether regular duct cleaning is beneficial or detrimental. See the entry Duct for more information.