How Often Should You Replace Your Furnace Filter?

Standard 1-inch fiberglass or pleated filters should be checked monthly and usually changed every 1 to 3 months. Thicker 4-inch and 5-inch media filters typically last 6 to 12 months.

The same filter serves both your furnace and central AC, since they share the same air handler and ductwork. That means the filter works year-round, not just in winter.

Pets, allergies, renovations, and dusty environments all shorten filter life. A home with two shedding dogs may need a fresh filter monthly, while a tidy condo might stretch closer to three months.

Running the fan continuously, common in summer for even cooling, also loads the filter faster. When in doubt, hold the filter up to a light; if you cannot see through it, replace it.

A clogged filter restricts airflow, which forces the blower to work harder, raises energy bills, and reduces comfort. In summer it can freeze the AC coil; in winter it can cause a furnace to overheat and shut down on a limit switch.

Most no-heat and no-cool service calls we see could have been avoided with a clean filter and a quick seasonal check.

The filter size is printed on the frame (for example 16x25x1). Buy the exact size so air cannot bypass the filter around the edges.

A MERV 8 to 11 filter balances filtration and airflow for most homes. Very high MERV filters can over-restrict airflow in older systems, so match the rating to what your equipment can handle.