Short answer
Use the filter size printed on your current filter's frame, and a MERV 8-11 pleated filter suits most homes. Check it monthly in winter and change 1-inch filters every 1-3 months. A clogged filter restricts airflow, overheats the furnace and is one of the most common causes of short cycling and shutdowns.
Find the right size
The size (for example 16x25x1) is printed on the filter frame. Thicker media filters (4-5 inch) last longer.
MERV ratings
Higher MERV catches more particles but restricts airflow more. Very high MERV in a system not designed for it can cause problems.
- MERV 8: good basic filtration
- MERV 11: better for pets and allergies
- MERV 13+: check with a technician first
Not sure it is safe to keep running? A local technician can check it today.
Call NowHow often
1-inch filters: every 1-3 months. Media filters: every 6-12 months. More often with pets or renovation dust.
Airflow arrow
Install with the arrow pointing toward the furnace, in the direction of airflow.
Related questions
Can a dirty filter stop my furnace?
Yes. It can trip the high-limit switch, causing the furnace to shut off repeatedly.
Are washable filters good?
They work but must be cleaned regularly and usually filter less than pleated filters.
Services that fix this
Furnace Tune-Up & Maintenance
Cleaning, safety checks and combustion testing before winter.
Furnace tune-up in Marlborough
Furnace Repair
Gas and oil furnaces that will not heat, blow cold, short-cycle or make noise.
Furnace repair in MarlboroughThis guide is general information for homeowners, not a diagnosis of your system. For anything involving gas, carbon monoxide, electricity or active leaks, stop and call a qualified professional.
