How to Change Your Furnace or HVAC Filter
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Quick answer: Turn the system off, slide out the old filter and copy the size printed on its edge, then put the new one in with the airflow arrow pointing toward the furnace/air handler (away from the return grille). ENERGY STAR says check it every month and change it at least every 3 months, sooner if it looks dirty.
⚠ Safety first:
- Turn the system off at the thermostat before opening the filter slot.
- Gas furnace? Have working carbon monoxide (CO) alarms. CO is colorless and odorless (EPA); if a CO alarm sounds or you feel headache, dizziness or nausea at home, get outside and call 911 or your gas utility.
- EPA recommends a trained professional inspect, clean and tune up furnaces, flues and chimneys every year.
Steps: easiest & free first
- Turn off the systemFREE · 1 min
Set the thermostat to off. - Find the filterFREE · 5 min
Usually in a slot at the furnace or air handler, or behind a return-air grille on a wall or ceiling. - Read the sizeFREE
The size is printed on the old filter’s frame; take a photo. - Buy the same sizeSHOP
Get the same size, and a MERV rating your system can handle (see MERV explained). - Install arrow toward the blowerFREE · 2 min
The arrow shows airflow; it points away from the return and toward the furnace. - Set a reminderFREE
Check monthly; change at least every 3 months (ENERGY STAR). - Call a pro if it acts upPRO
See below.
⚠ When to call a pro: a CO alarm goes off; you smell burning, gas or electrical odors; the furnace short cycles (turns on and off rapidly) or overheats after a filter change; ice on the A/C coil; or you want a higher-MERV filter and aren’t sure your system can handle it (EPA suggests asking an HVAC technician). Have a pro tune up the system each year (EPA). Renting? See what you can fix vs. call your landlord.
Helpful supplies
| Item | Why | |
|---|---|---|
| Replacement HVAC filter (your size) | Match the size printed on the old one | Check price [PLACEHOLDER – no affiliate link] |
Generic categories only; check the product label and your home’s needs before buying.