Find

Furnace air filter — turn the system off before you swap

Furnace filter

Set the thermostat to off before a furnace air filter swap, so the blower does not pull loose dust past the open slot while the filter is out.

close-up of a pleated air filter panel
Photo: No machine-readable author provided. SpLoT assumed (based on copyright claims). / Wikimedia Commons (CC BY 2.5)

Before you pull a furnace air filter, switch the thermostat to off. With the slot open, a running blower pulls dust straight into the system.

Turn the system off before a furnace air filter swap

  1. Set the thermostat to off (not just a lower temperature).
  2. Wait until the blower stops before opening the filter door.
  3. Swap the filter with the airflow arrow pointing toward the furnace and close the door.
  4. Set the thermostat back to your normal mode.

Honest stop: if the blower keeps running with the thermostat off, it may be set to fan-on — switch the fan to auto too.

Before you slide the new one in, check which way the arrow goes: it points toward the furnace, or into the wall or ceiling at a return grille.

More help