1Find the filter
Look in the slot next to the furnace or air handler, or behind a return grille in a wall or ceiling.
FREE REPAIR GUIDE
How to Change a Furnace or AC Filter
Change your HVAC air filter in 5 minutes: find the size, the airflow arrow, and how often to replace it.
DIFFICULTYVery easy
ESTIMATED TIME~5 min
TOOLSNone
POTENTIAL SAVINGSEnergy & repairsLabour estimate · varies
Know what you’re replacing.
A clogged filter makes your furnace and AC work harder, raises energy bills, and can cause the system to overheat or freeze up. Changing it takes five minutes. Check it every 1–3 months.
What you’ll need.
HVAC air filter (MERV 8–11)Match the size printed on your old filter, e.g. 16x25x1 · ~$10–20
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A little preparation first.
- Turn the thermostat off.
- Read the size printed on the edge of the old filter.
One step at a time.
2Turn the system off
Switch the thermostat to Off so the blower doesn't pull dust in.
3Slide out the old filter
Slide the old filter out and note the arrow direction.
4Insert the new filter
Insert the new filter with the arrow pointing toward the furnace (in the direction of airflow).
5Turn it back on
Turn the system back on and write the date on the filter edge.
Log in 
Troubleshooting
Filter whistlesToo restrictive (very high MERV) or wrong size; use the correct size and MERV 8–11.AC coil freezingA clogged filter is a common cause — replace it and let the ice melt.Still no heat or coolingCheck the thermostat batteries and breaker, then run a diagnosis.
FAQ
How often?Every 1–3 months; monthly with pets or allergies.Washable filters?Some are, but most homes use disposable pleated filters.
General guidance only. Turn off power, water or gas before you work and follow the manufacturer’s instructions; if unsure, call a qualified professional.