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Change a furnace or HVAC filter

A clean filter lets your heating and cooling system move air without straining. Swapping it takes a few minutes and needs no tools in most homes.

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Last reviewed against 3 official sources.

Who this is for

Anyone with forced-air heating or central air, whether you own or rent. Renters: check your lease, the filter is often your job.

How often should I change my furnace filter?

ENERGY STAR says to check the filter every month, especially in winter and summer when the system runs most, and to change it when it looks dirty. Change it at least every 3 months.

From: ENERGY STAR (U.S. Environmental Protection Agency)

What you need

Tools

  • A step stool if the filter sits in a ceiling or high wall grille

Supplies

  • A new filter the same size as the old one (the size is printed on the filter’s frame)

Steps

  1. Turn the system offSet the thermostat to Off so the fan does not run while the filter is out.
  2. Find the filterIt sits behind a return-air grille on a wall or ceiling, or in a slot beside the furnace or air handler. Your system’s manual shows where.
  3. Note the size and the arrowRead the size printed on the old filter’s frame and look at which way its airflow arrow points before you pull it out.
  4. Slide the old filter outHold it up to a light. If it looks dirty, replace it.
  5. Slide the new filter inPoint the arrow the same way as before: toward the furnace or air handler, the way the air flows.
  6. Close up and turn the system onShut the grille or slot cover, then set the thermostat back.
  7. Write down the dateNote the date and the filter size so the next change is quick.

Safety notes

  • Do not run the system with no filter in place.
  • Leave the burner access door on a gas furnace closed. The U.S. Fire Administration says to keep those doors shut so flames cannot escape.
  • If you smell gas, leave the home and call your gas company from outside.

When to call a professional

  • ENERGY STAR recommends a yearly tune-up of heating and cooling equipment by a contractor.
  • If the system is more than 10 years old or is not keeping the house comfortable, ENERGY STAR suggests having a professional evaluate it.
  • Anything involving the gas line, burner or wiring is a job for a licensed technician.

Sources

This guide is general information written in our own words from the sources above. Your owner’s manual and the instructions for your own equipment come first.

Tell it once. It remembers.

Check monthly and change it when dirty, at least every 3 months.

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