1- Air Quality
Air filtration is one of the least expensive ways to improve air quality. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) suggests that filters should be cleaned or replaced not less than every 3 months.
2- Equipment efficiency
According to the US Department of Energy’s Federal Energy Management Program, air filters play a critical role in maintaining indoor air quality and protecting the downstream components of the cooling equipment (coils, blower, etc) from accumulating dirt that reduces equipment efficiency.
3- Contamination source
A dirty filter can become a contamination source if not cleaned or replaced. Dirty filters can also force air to go around and bypass filtration sections and the unfiltered bypass air deposits debris on the cooling/heating coils rather than on the filter.
Routinely change or replace filters based on either regular intervals or by visual inspection. Intervals can range from 1-6 months (some newer type and style filters indicate usage up to 6 months), depending on the dirt loading from both the indoor and outdoor air. Visual inspections of the leading edge side of the filters can help indicate frequency. In commercial facilities, measuring the pressure drop across the filter is the most reliable way to rate particulate loading on the filter.