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20x20x1 furnace filter

Sizes, MERV guidance and a replacement schedule for 1-inch 20x20x1 air filters.

Nominal size20 x 20 x 1 inprinted on the frame
Actual size19.5 x 19.5 x 0.75 inFilterBuy listing
Check / replace~every 3 monthstypical; check monthly
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When to replace

Carrier: a 1-inch filter may need changing about monthly; Carrier generally recommends about every three months depending on use. Check monthly. Pets, allergies, construction dust and heavy heating/cooling use all shorten the interval.

Set it and forget it. Add your 20x20x1 to My house and get an email when it's due.

Choosing a MERV rating

MERV (Minimum Efficiency Reporting Value) reports a filter's ability to capture particles between 0.3 and 10 microns; higher MERV traps more of specific particle sizes. EPA: if upgrading, choose at least MERV 13 or as high as your system fan and filter slot can accommodate; you may need an HVAC technician to confirm.

RatingAverage capture efficiency (EPA)
MERV 1-43.0-10.0 µm: less than 20%
MERV 53.0-10.0 µm: ≥20%
MERV 63.0-10.0 µm: ≥35%
MERV 73.0-10.0 µm: ≥50%

Table excerpt; see EPA for MERV 8-16.

FAQ

What is the actual size of a 20x20x1 filter?

Nominal 20x20x1 filters are slightly smaller than the label so they slide in; FilterBuy lists this size at 19.5 x 19.5 x 0.75 inches. Exact dimensions vary a little by brand.

How often should I change a 20x20x1 filter?

Carrier: a 1-inch filter may need changing about monthly; Carrier generally recommends about every three months depending on use. Check monthly. Follow your HVAC manufacturer's recommendation.

Which MERV rating should I buy?

MERV (Minimum Efficiency Reporting Value) reports a filter's ability to capture particles between 0.3 and 10 microns; higher MERV traps more of specific particle sizes. EPA: if upgrading, choose at least MERV 13 or as high as your system fan and filter slot can accommodate; you may need an HVAC technician to confirm.

Sources

Data checked 2026-10-17. Always confirm the part number printed on your current filter or in your owner's manual.