How often should you change your furnace filter?

A dirty furnace filter does not just make air dusty. It can reduce airflow, make the blower work harder, and let more particles recirculate through the house. The right replacement schedule depends on filter thickness, filter type, and how hard your system runs.

As a practical baseline, check the filter every month. A thin 1-inch fiberglass filter may need replacement about every 30 days. A 1-inch pleated filter often lasts 30 to 90 days. A thicker media filter in a dedicated cabinet can last longer, but you should still inspect it instead of relying only on the calendar.

Change it sooner if you have pets, allergies or asthma in the house, wildfire smoke, renovation dust, a smoker, or a season when the furnace or AC runs nearly nonstop. The quick test is visual: if the filter looks gray, matted, or clogged, replace it. If rooms feel weaker at the vents than usual, check the filter before assuming the equipment is failing.

Do not automatically buy the highest-MERV filter on the shelf. Very dense filters can restrict airflow in systems not designed for them. Match the size and rating your HVAC system can handle, and keep a spare furnace filter on hand so replacement is not a separate errand.