Furnace filter finder

Find the filter that fits your slot, at a MERV your system can take.

Furnace filters are sold by a nominal size that is not what the filter measures, and rated by a MERV number that your system may or may not tolerate. Tell us the slot and the system, and this narrows it to what actually fits and what your blower can take.

What size is printed on your current filter?

The number on the cardboard edge - that is the nominal size, and it is what you order by. Measure only if the print has worn off.

20x25x1The most common one-inch size.12x24x1An uncommon size - fewer options, so order early.Something elseWe do not stock a match for that slot yet.

How much filtration do you need?

The most a 1-inch slot allowsMERV 13. The EPA suggests at least MERV 13, or as high as your system will accommodate.A balance of filtration and airflowMERV 11. Meaningful filtration with less restriction than MERV 13.

How old is the system?

Restriction matters more on an older blower. This changes what we recommend, not what fits.

Under about 10 yearsLikely to tolerate a higher MERV.Older, or it already strugglesWeak airflow, short cycling, or a coil that has frozen before.

Questions about this tool

Why is a 20x25x1 filter not 20 by 25 inches?

Nominal size is the ordering size; actual size is what it measures, and it is always slightly under so the filter slides into the slot. The two 20x25x1 filters on this site measure 19.62 x 24.62 x 0.78 and 19.75 x 24.75 x 0.75 - both sold as the same size, an eighth of an inch apart.

Should I just buy the highest MERV I can find?

The EPA suggests a filter rated at least MERV 13, or as high as your system will accommodate. That last clause is the important half: a higher MERV in a one-inch slot restricts more airflow, and a system that cannot move air through it will underperform whatever the filter is rated.

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