Ask an Expert: Dirty Air Filters and Energy Use

Does my home heating and cooling system use more energy if the filter is dirty?

The primary job of an air filter is to keep dirt and dust off the fan blades, motor and cooling coils. Surprisingly, a dirty filter doesn't have much of an impact on overall air conditioning or furnace operating costs. That's because the air flow is not significantly changed unless the filter becomes really clogged. Also, air tends to find a way around dirty filters. Finally, dirt on the coils may simply reduce system capacity, causing it to run longer, but with little impact on costs.

So, changing your filter regularly according to manufacturer's instructions can improve indoor air quality and extend the life of heating and cooling system components, but it will not significantly reduce your heating and cooling costs.