Furnace Filter Calculator
Type the size printed on your current filter frame, pick how often you will actually change it, and set the price per filter. You get the yearly cost, the next change date, and a straight answer on MERV ratings.
The filter aisle sells fear in both directions - premium MERV 13 for everyone, or 1-dollar fiberglass that filters almost nothing. The honest version: MERV 8 for dust, 11 for pets and allergies, 13 only if your system is rated for the airflow drag, which otherwise arrives on your bill as longer runtimes.
How to use
- Read the nominal size off the frame edge - numbers like 16x25x1.
- Set the interval honestly; peak heating season is usually 30 days for 1-inch filters.
- Check the lamp test monthly: no light through the filter means change it now.
Frequently asked questions
What size furnace filter do I need?
The nominal size printed on your current filter frame - something like 16x25x1. The actual frame is about half an inch smaller on each side; buy by the nominal number and the cardboard edge compresses to seal. If the print is gone, measure the slot and round up to the nearest nominal size.
How often should I change my furnace filter?
Every 30 days in peak heating or cooling season, 60-90 in shoulder months for 1-inch filters. Pets, wildfire smoke and a dusty renovation shorten it. The calendar is a floor - hold it up to a lamp and let your eyes make the call.
What MERV rating should I use?
MERV 8 for most homes, MERV 11 with pets or allergies, MERV 13 only if the system manual says it can breathe through one. Higher ratings catch smaller particles but fight the blower, and the cost shows up as longer runtimes, not on the filter price tag.
What happens if I never change the filter?
Airflow drops, the blower works harder, the heat exchanger runs hotter, and in the worst case the limit switch starts short-cycling the furnace. It is the cheapest maintenance in the house and the most common cause of no-heat calls in January.