Cheap fiberglass filters do very little to improve the air quality in the home. The layer of fiberglass is not nearly thick enough to capture anything but large particles of dust. Many of the most harmful microorganisms are virtually invisible, and require a much more efficient filter in order to be collected. Upgrading the furnace filter to one with a MERV rating above 8 or 9 could drastically improve indoor air quality, but there is one problem. These filters still need to be changed every 2-3 months and the extra cost of the upgrade is simply not practical for many homeowners.