Furnace filters are devices that protect the mechanical system of a furnace from particulate materials. While a fiberglass fiber filter provides enough protection for most furnaces, higher quality filters also help clean the air to protect the health of the home occupants.
Consumers have several choices in the types of filter they install in their furnace. While the disposable fiber or cellulose filter protects the furnace, it does little to protect the lungs, according to the University of Illinois Extension. Pleated filters offer better filtration and still fit into the normal filter holder. Deep pleated filters and electronic filters offer better cleaning of the air but require modification of the filter box.
Fiber filters only remove 2 percent of the smallest dust particles from the air, while electronic filters remove up to 94 percent. The other choices fall in the range between these two levels. A good filter reduces allergens, pollen and dust in the air.
Most furnace manufacturers recommend replacing or cleaning the filter on the HVAC unit every three months. Filters with cardboard frames are disposable, but the manufacturer expects the owner to clean those with other types of frames. In homes with pets or smokers, filters require replacement as frequently as every month. Leaving a dirty filter in place reduces the efficiency of the system and compromises the air quality.