How do dirty air filters impact heating and cooling system performance?

A dirty filter will slow down air flow, making your heating or cooling system work harder to maintain a comfortable temperature. This wastes energy and increases your utility costs.

Researchers at North Carolina A&T State University investigated the impact of air filter pressure drop on the performance of typical air-conditioning systems.

With a constant-speed fan, the cooling energy use increases as the filter gets dirty over time and the energy use in the fan may increase. With a variable-speed fan, the fan energy use increases with a dirty filter but the cooling and heating energy uses are only slightly affected.

Also, air filters protect the components of your heating and cooling system, including coils and fans, from accumulating dirt, which can reduce equipment performance and indoor air quality. According to Coil-Tech, if a rooftop unit evaporator coil gets clogged and airflow is restricted by one-third, the capacity drop is 20%. This changes the 3-ton unit to a 2.5-ton unit, for instance.

If the filter becomes too dirty, air will go around the filtration section and deposit dirt directly on system components. This can increase maintenance costs significantly because more time and expertise are required to clean system components than what's needed to change filters.

The U.S. Department of Energy recommends that you check filters once a month, especially during periods of heavy use, such as winter and summer. If the filter is dirty, change it. At a minimum, conventional filters should be changed once every three months. Other types of filters need less frequent replacement. Check manufacturer's recommendations for guidance.