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.
Change schedule by home
Filter life depends on dust, pets, occupants and run time.
- 1-inch filter, no pets: about every 60 days
- 1-inch filter with pets or allergies: about every 30 days
- 2-inch pleated: about every 2–3 months
- 4–5 inch media: about every 6–12 months
- Check monthly during heavy dust, smoke or peak cooling
Fiberglass, pleated or washable?
Inexpensive fiberglass panels mainly protect the equipment and catch large debris. Pleated filters catch much finer particles and are the usual choice for homes. Washable filters must be fully dry before reinstalling and generally capture less fine dust than pleated filters.
Signs your filter is too restrictive
A filter can be too efficient for the system it's in.
- Whistling at the return grille
- Weak airflow at registers
- Coil freezing after switching to a higher MERV
- Filter bowing or pulling out of its slot
Multiple returns, multiple filters
Some homes have more than one return grille with a filter in each. All of them need changing on the same schedule; a forgotten second filter can restrict the whole system.
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.
What does MERV stand for?+
Minimum Efficiency Reporting Value, a rating from 1 to 16 that describes how well a filter captures particles of different sizes. Higher numbers capture smaller particles.
Is MERV 13 too high for my system?+
It depends on the blower and duct design. In deep media cabinets it usually works well. In a 1-inch slot it can restrict some systems, so watch for weak airflow or ask a tech to measure static pressure.
Do I need to turn the system off to change the filter?+
It's best to. Turning the system off keeps dust from being pulled past the open slot.
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.