How to Replace a Furnace Filter
To replace a furnace filter: turn off the system, find the filter slot on the return-air side of the furnace, slide out the old filter, note the airflow arrow direction, and slide in the new same-size filter with the arrow pointing toward the furnace/blower. Turn the system back on. The whole job takes under five minutes.
Step-by-step replacement
- Turn off the furnace at the thermostat or switch.
- Locate the filter slot — usually where the return duct meets the furnace, or behind a return grille.
- Slide out the old filter and note the printed size and airflow arrow.
- Insert the new filter with the airflow arrow pointing toward the furnace (direction of airflow).
- Close the cover and turn the system back on.
Which way does the arrow point?
The airflow arrow on the filter frame must point in the direction the air flows — that is, toward the furnace and blower, away from the return duct. Installing a filter backwards reduces efficiency and can damage the media.
Frequently Asked Questions
Which way does a furnace filter go in?
The airflow arrow printed on the filter frame should point toward the furnace/blower, in the same direction the air is moving (from the return duct into the furnace).
Do I need to turn off the furnace to change the filter?
It's best practice to turn it off so the blower isn't pulling air while the slot is open. It only needs to be off for the minute or two it takes to swap the filter.
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