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Trane S8X1 / S8X2 gas furnace: filter size

The Trane S8X1 / S8X2 gas furnace uses a 14 x 25 x 1, 16 x 25 x 1, 20 x 25 x 1 or 24 x 25 x 1 filter, depending on cabinet width (or model) and return location (per the Trane document cited on this page). The table below shows which size applies to each cabinet and return.

Verified from manufacturer doc 1-stage / 2-stage induced-draft gas furnaces; filters installed externally

Last checked against the manufacturer document:

Applies to

Model numbers printed in the linked Trane document:

S8X1A026M2PSAB, S8X1A040M3PSAB, S8X1B040M2PSAB, S8X1B060M3PSAB, S8X1B060M4PSAB, S8X1B080M4PSAB, S8X1C080M5PSAB, S8X1C100M5PSAB, S8X1D120M5PSAB, S8X2A040M3PSAB, S8X2B060M3PSAB, S8X2B060M4PSAB, S8X2B080M4PSAB, S8X2C080M5PSAB, S8X2C100M5PSAB, S8X2D120M5PSAB

Filter sizes by cabinet / model

Furnace widthFilter qty and size
14-1/2 in.1 – 14 x 25 x 1
17-1/2 in.1 – 16 x 25 x 1
21 in.1 – 20 x 25 x 1
24-1/2 in.1 – 24 x 25 x 1

For upflow furnaces whose airflow requirement exceeds 1600 CFM, Trane requires return openings and filters on both sides, one side plus the bottom, or the bottom only. Filters are not factory supplied and are installed externally.

Measuring a furnace air filter's edge with a tape measure
Illustration only. Not this manufacturer's part.

Replacement interval

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.

Before you buy

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.

Buy

Match the size or part number printed on your current filter.

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MERV notes

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.

Related models

Where this data came from

Installer's Guide 18-CE04D1-1D-EN, Return Air Filters table
Last checked 2026-10-26. Manufacturers revise documents. If your unit's label disagrees, trust the label.

FAQ

What size filter does the Trane S8X1 / S8X2 gas furnace use?

The Trane S8X1 / S8X2 gas furnace uses a 14 x 25 x 1, 16 x 25 x 1, 20 x 25 x 1 or 24 x 25 x 1 filter, depending on cabinet width (or model) and return location (per the Trane document cited on this page). The table below shows which size applies to each cabinet and return. 14-1/2 in. – 1 – 14 x 25 x 1; 17-1/2 in. – 1 – 16 x 25 x 1; 21 in. – 1 – 20 x 25 x 1; 24-1/2 in. – 1 – 24 x 25 x 1.

How often should I replace the Trane S8X1 / S8X2 gas furnace filter?

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.

Why doesn't my filter measure exactly 16 x 25?

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.

What filter size does the Trane 14-1/2 in. use?

1 – 14 x 25 x 1 (per the Trane source table).

What filter size does the Trane 24-1/2 in. use?

1 – 24 x 25 x 1 (per the Trane source table).

Where does this information come from?

Installer's Guide 18-CE04D1-1D-EN, Return Air Filters table (https://elibrary.tranetechnologies.com/public/residential-hvac/Literature/Installation/18-CE04D1-1D-EN_05082020.pdf), last checked 2026-10-26.