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Did You Clean That? · No. 04

Your AC Air Filter: the one-page checklist

Things everybody uses. Almost nobody cleans.

Check these parts

  • Filter size printed on the frame
  • Airflow arrow direction
  • Return vent or air handler slot
  • Date you last changed it

What you need

  • The correct replacement filter, matched to the size printed on the old one
  • A marker to date the new filter
  • A vacuum for the vent grille
  • Your system's owner manual for the recommended filter type and schedule

Do it in this order

  1. 01. Turn the system off. Switch the thermostat to off so the blower is not pulling air while the slot is open.
  2. 02. Find the filter. It sits either behind a large return air grille on a wall or ceiling, or in a slot at the air handler or furnace. Check your manual if you are not sure.
  3. 03. Read the old filter before you toss it. The size is printed on the cardboard frame, something like 20x25x1. Take a photo of it.
  4. 04. Note the airflow arrow. There is an arrow on the frame. It points toward the blower, away from the return. The new one goes in the same direction.
  5. 05. Vacuum the grille and slot. A quick pass while it is open, so you are not pulling that dust straight into the new filter.
  6. 06. Slide the new filter in and date it. Arrow the same way as the old one. Write the date on the frame with a marker, close the grille, turn the system back on.

Don't do this

  • · Don't force a filter that doesn't fit. Air will bypass the gap and the filter does nothing.
  • · Don't install it backward. The arrow points toward the blower.
  • · Don't wash a disposable filter. Washable filters are a different product and must be fully dry before reinstalling.
  • · Don't jump to the highest-rated filter without checking your manual. Some systems are not designed for very restrictive filters.

Know when to stop

If the system is still short cycling, freezing up or blowing warm after a fresh filter, that is a service call. A filter fixes airflow, not refrigerant or electrical problems.

LaLa says

“This is a five dollar part and a two minute job. Write the date on the edge of the filter with a marker so future you does not have to guess.”