Do I Need to Replace My Furnace Filter in Summer?

Short answerYes, if your central AC shares the furnace's blower and ducts, because we expect the same filter serves both. ENERGY STAR says to check filters every month and clean or change them when dirty. DOE says a clogged filter restricts airflow and reduces cooling. If you only use the furnace in winter with separate cooling, ask your installer.

Why summer still counts

We expect that with central air, the blower pulls air through your filter whenever it runs. DOE says a clogged filter restricts airflow through the unit and cuts its ability to cool the air. ENERGY STAR adds that a dirty filter can raise energy costs and cause early equipment failure.

How often

ENERGY STAR says to inspect, clean or change filters once a month. NC State Extension says some may need monthly changes. That doesn't mean every filter needs replacing monthly. Check it, and follow what the filter's maker says if it looks clean. We expect homes with pets or dust may see filters get dirty faster, though we didn't find an official figure for that.

If you don't run central AC

We expect that with window units or mini-splits and a furnace off for the summer, little air may move through the furnace filter. We'd check it anyway before heating season. ENERGY STAR suggests a heating check-up with a contractor in fall, and a cooling check-up in spring.

Furnace Won't Turn On? Safe Checks Before You Call

Common questions

Does a dirty filter cause an AC to freeze?

Trane says a dirty filter can cause freezing. If you see frozen coils, Trane says to turn the system off and contact an HVAC professional. Replace a dirty filter too.

How do I find my filter?

We expect it's in a slot at the furnace or behind a return air grille. We recommend asking a contractor to show you.

Do I Need to Replace My Furnace Filter in Summer?

Why summer still counts

How often

If you don't run central AC

Common questions

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