PadMatch / Every humidifier water panel and furnace filter size
- Nominal size
- 20 x 20 x 1 in
- Actual size
- 19.5 x 19.5 x 0.75 in
- Depth class
- 1 in (flat panel)
- Typically installed on
- square return grilles and some horizontal air handlers
- Sold in MERV
- sold flat-panel in MERV 8, 11 and 13
Nominal versus actual dimensions for the 20 x 20 x 1 in furnace and HVAC air filter.
A 20 x 20 x 1 in furnace filter has an actual size of 19.5 x 19.5 x 0.75 in. The label is the nominal size, rounded up so the filter is easy to name; the panel is cut undersize so it slides into the slot without binding.
A square flat filter, actual 19.5 by 19.5 by 0.75 inches. Because it is square, it can be installed in either rotation, which is why a 20 by 25 slot will not accept it and vice versa.
Order by the nominal size printed on the old filter frame, not by measuring the slot, because every brand runs to the same nominal-to-actual convention.
Find your model
Read the number stamped on the humidifier cabinet or printed on the old pad, then match it below. Confirm the frame size before buying a generic.
- 20 x 20 x 1 in actual sizenominal vs actual dimensions
- 16 x 25 x 1 in furnace filteractual 15.5 x 24.5 x 0.75 in
- 20 x 25 x 1 in furnace filteractual 19.5 x 24.5 x 0.75 in
- MERV 8 vs 11 vs 13 for a furnace filterwhich rating to buy
Sources: Atomic Filters nominal vs actual air filter size chart ยท Filterbuy air filter sizes chart