How often should I change my air filter?

Updated October 2026 · How we answer

Typical replacement schedule

A common rule is every 30 to 90 days for standard 1-inch fiberglass or pleated filters. If you have pets, allergies, or live in a dusty area, change it every 30 to 45 days. Homes with no pets and low dust may stretch to 3 months.

Thicker filters (4 to 5 inches) often last 6 to 12 months. Check the manufacturer's recommendation on the filter frame. Some smart thermostats or filter indicators can remind you, but they are not always accurate.

• 1-inch filter: every 1–3 months
• Pets or allergies: every 30–45 days
• Thick 4–5 inch filter: every 6–12 months
• Check filter monthly for visible dirt

Factors that change the schedule

Run your HVAC system more often during heating or cooling season, and you'll need to change the filter more frequently. Construction or renovation dust, wildfire smoke, and high pollen counts also shorten filter life.

If you use a washable or reusable filter, clean it according to the manufacturer's instructions—usually every 1 to 3 months. Never put a wet filter back into the system.

• More runtime = more frequent changes
• Renovation or smoke = change sooner
• Washable filters: clean every 1–3 months
• Never install a damp filter

How to check and replace

Turn off the system before removing the filter. Hold it up to a light: if you can't see light through it, it's dirty. Also look for gray fuzz, dust buildup, or a musty smell. A clogged filter makes your system work harder and can raise energy bills.

Note the size printed on the old filter (e.g., 20x25x1). Install the new one with the arrow pointing toward the furnace or air handler. Write the date on the new filter to track when to change it next.

• Turn off HVAC before changing
• Hold up to light to check for clogging
• Match size and airflow arrow direction
• Write the date on the new filter

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