How to change the air filter in your furnace
Changing a furnace air filter takes five minutes. Turn the system off at the thermostat, then look behind the big return vent grille or in the slot beside the furnace. Note the size printed on the edge of the old filter, buy that exact size, and slide the new one in with its arrow pointing the way the air moves, toward the furnace. Set a reminder for the next change.
Why it matters: A clogged filter makes the heat and air conditioning work harder and circulate more dust.
Steps
- Switch the heating and cooling off at the thermostat.
- Look for the filter behind a large wall or ceiling return grille, or in a slot on the furnace.
- Slide out the old filter and copy the size printed on its edge.
- Buy the same size in the type your system's manual or landlord recommends.
- Slide the new filter in with the arrow on its edge pointing toward the furnace.
- Put the grille back and turn the heating and cooling on again.
- Write the date on the new filter and set a phone reminder to check it in a month.
Common mistakes
- Putting the filter in with the arrow backward.
- Buying a size that is close but not exact.
- Forgetting the filter for a whole season.
- Opening the burner or blower panels; changing the filter is the only job here.
Teach this to someone
A one page sheet for showing a friend, a teenager or a parent: what to say, what to show, and one question to check it landed.
Teach: How to change the air filter in your furnace
What to say
Changing a furnace air filter takes five minutes. Turn the system off at the thermostat, then look behind the big return vent grille or in the slot beside the furnace. Note the size printed on the edge of the old filter, buy that exact size, and slide the new one in with its arrow pointing the way the air moves, toward the furnace. Set a reminder for the next change.
What to show
- Switch the heating and cooling off at the thermostat.
- Look for the filter behind a large wall or ceiling return grille, or in a slot on the furnace.
- Slide out the old filter and copy the size printed on its edge.
- Buy the same size in the type your system's manual or landlord recommends.
- Slide the new filter in with the arrow on its edge pointing toward the furnace.
- Put the grille back and turn the heating and cooling on again.
- Write the date on the new filter and set a phone reminder to check it in a month.
Check question
Where does the arrow on a furnace filter point?
Answer: Toward the furnace, the way the air moves. The filter is built to catch dust from one direction.
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Related skills
Sources
- US federal home energy saving guidance, 2025. Reviewed September 28, 2026.
Written in our own words from the sources above. It is general information, not advice for your situation; where a professional, your doctor or your lease says something different, follow them.
Last reviewed . First published .