Short answer
Use the size printed on your current filter's frame and a MERV 8 to 11 for most 1-inch slots. Change 1-inch filters every 30–60 days in Las Vegas, more often during dust season or with pets. Deep 4–5 inch media filters last 6–12 months.
Find the size
The frame shows nominal and actual sizes. Some homes have filters in return grilles in hallways or ceilings; others at the air handler.
Pick a MERV
Higher isn't always better for thin filters.
- MERV 8: good baseline
- MERV 11: better for fine dust and pets
- MERV 13: smoke and allergies, best in deep media cabinets
Airflow arrow
The arrow points toward the blower, away from the return grille.
Questions
Can a dirty filter break my AC?+
It can cause frozen coils, overheated motors and higher bills, and it's a leading cause of avoidable service calls.
Editorial note: this guide is general information for homeowners, not a diagnosis. Desertline Heating & Air is a referral service; a licensed contractor should inspect your equipment before repairs.