Nearly half of the energy used in your home goes to heating and cooling. So making smart decisions about your home’s heating, ventilating, and air conditioning system (HVAC) can have a big effect on your utility bills — and your comfort.

Inspect, clean, or change air filters once a month in your central air conditioner, furnace, and/or heat pump, especially during heavy use months (winter and summer). If the filter looks dirty after a month, change it. At a minimum, change the filter every three months. A dirty filter will slow down air flow and make the system work harder to keep you warm or cool — wasting energy. A clean filter will also prevent dust and dirt from building up in the system — leading to expensive maintenance and/or early system failure.

https://www.energystar.gov/campaign/heating_cooling