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The Goodman GM9S80 (ultra-low NOx) gas furnace uses one of 3 filter sizes, depending on cabinet width (or model) and return location: 16x25, 14x24, 20x25 (per the Goodman document cited on this page). The page's table shows which size applies to each cabinet and return.
Verified from manufacturer doc 80% AFUE single-stage, multi-speed ECM
| Model | Minimum filter size(s) |
|---|---|
| GM9S800403AU / 0603AU | (1) 16 x 25 (side) or (1) 14 x 24 (bottom) |
| GM9S800604BU / 0804BU | (1) 16 x 25 (side or bottom) |
| GM9S800805CU | (2) 16 x 25 (side) or (1) 20 x 25 (bottom) |
Goodman: larger filters may be used, and filters may be centrally located. Footnote: use 2 x 16x25 (side) or 20x25 (bottom) if connected to a cooling unit over 4 tons.
General guidance (not from this manual): check monthly and replace 1-in. filters every 1–3 months, or follow the filter maker's guidance and your owner's manual.
Pull the old filter and read the size printed on its frame. Nominal sizes are rounded up: a 15.5 x 24.5 in. filter is sold as 16 x 25.
Your furnace manual lists the filter's dimensions, not its MERV rating. Higher-MERV filters restrict more air. Manufacturers such as Carrier recommend keeping the clean-filter pressure drop under 0.2 in. w.c. (ideally under 0.1). Lennox warns that an over-restrictive filter can trip the high limit in winter and freeze the coil in summer. If you want MERV 11–13, a 4-in. media cabinet is the usual route. Ask an HVAC tech to check static pressure. Nominal sizes are rounded: a filter labeled 16 x 25 x 1 actually measures about 15.5 x 24.5 x 0.75.
SS-GM9S80-U specification sheet (10/21), Minimum Filter Sizes
Last checked 2026-10-21. Manufacturers revise documents. If your unit's label disagrees, trust the label.
The Goodman GM9S80 (ultra-low NOx) gas furnace uses one of 3 filter sizes, depending on cabinet width (or model) and return location: 16x25, 14x24, 20x25 (per the Goodman document cited on this page). The page's table shows which size applies to each cabinet and return. GM9S800403AU / 0603AU – (1) 16 x 25 (side) or (1) 14 x 24 (bottom); GM9S800604BU / 0804BU – (1) 16 x 25 (side or bottom); GM9S800805CU – (2) 16 x 25 (side) or (1) 20 x 25 (bottom).
General guidance (not from this manual): check monthly and replace 1-in. filters every 1–3 months, or follow the filter maker's guidance and your owner's manual.
Filter sizes are nominal (rounded). A filter sold as 16 x 25 x 1 actually measures about 15.5 x 24.5 x 0.75 in. Buy by the nominal size printed on the frame.
SS-GM9S80-U specification sheet (10/21), Minimum Filter Sizes (https://documents.alpinehomeair.com/product/goodmangm9s80%2Duspecsheet%2Epdf), last checked 2026-10-21.