Where do I find my AC filter size?
Check the old filter edge first. If it is missing or wrong, check the return grille, filter cabinet, air handler label, or manual.
AC Filter Size and MERV Guide
The filter is the fastest safe AC tune-up step, but the wrong size, direction, or MERV rating can create airflow problems.
Where to Look
- Old filter edge
- Return grille
- Air handler or furnace filter rack
- Cabinet label
- System manual
- Previous service sticker or maintenance note
When to Replace More Often
- Pets
- Heavy dust
- Allergies
- Wildfire smoke
- Renovation dust
- High summer runtime
- Weak airflow after a dirty filter
Common Questions
What MERV rating should I use?
Many homes use MERV 8 to 11. Higher MERV can catch smaller particles but may restrict airflow if the system is not designed for it.
Can the wrong filter make my AC not cool?
Yes. A clogged, wrong-size, backwards, or overly restrictive filter can reduce airflow, which can hurt comfort and sometimes contribute to icing.
Related Summer HVAC Guides
Plan This Project in ChatDIY
ChatDIY can help identify your filter size, choose a reasonable MERV rating, and save it into the AC tune-up record.