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Trane S9X1 / S9X2 / S9B1 furnace: filter size

Trane S9X1 / S9X2 / S9B1 filter sizes: 16 x 25 x 1, 20 x 25 x 1 and 24 x 25 x 1, as listed in the Trane source document's filter table. Which size fits depends on your cabinet and return. This page is pending human review, so check the source excerpt below.

Auto-extracted · review pending Filter sizes auto-extracted from the manufacturer document.

Last checked against the manufacturer document:

Filter sizes by cabinet / model

Sizes found in the source table
16 x 25 x 1
20 x 25 x 1
24 x 25 x 1

Extracted by script from the linked document. Read the excerpt to see which size applies to which cabinet or return.

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.

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

Manufacturer document for Trane S9X1 / S9X2 / S9B1
Last checked 2026-11-04. Manufacturers revise documents. If your unit's label disagrees, trust the label.

Excerpt from the source

                                                                    requirement. Filters must be installed externally to the unit.
                                                                    Table 40.    Downflow return air filters
                                                                          Furnace Width (in.)           Filter Qty and Size (in.)
                  *
                                                                                 17–1/2                      1– 16 x 25 x 1
                            *
                                                                                  21                         1 – 20 x 25 x 1
                                                       FRONT                     24–1/2                      1 – 24 x 25 x 1
                                                       OF FURNACE
Note: See dimensional data drawing.                                 Electrical Connections
Return Air Filters for Furnace in Horizontal
                                                                    Make wiring connections to the unit as indicated on
Configuration
                                                                    enclosed wiring diagram. As with all gas appliances using
When the furnace is installed in the horizontal                     electrical power, this furnace shall be connected into a
configuration, the return air filters must be installed exterior    permanently live electric circuit. It is recommended that
to the furnace cabinet. Remote filter grilles may be used for       furnace be provided with a separate "circuit protection
homeowner convenience, see Figure 76, p. 60 or the filters          device" electric circuit. The furnace must be electrically
may be installed in the duct work upstream of the furnace,          grounded in accordance with local codes or in the absence
see Figure 77, p. 60.                                               of local codes with the National Electrical Code, ANSI/
Filter kits are available for horizontal applications.              NFPA 70, if an external electrical source is utilized. The
                                                                    integrated furnace control is polarity sensitive. The hot leg
Note: Direct coupled side returns are not allowed to the            of the 120V power supply must be connected to the black
      furnace cabinet.                                              power lead as indicated on the wiring diagr

FAQ

What size filter does the Trane S9X1 / S9X2 / S9B1 use?

Trane S9X1 / S9X2 / S9B1 filter sizes: 16 x 25 x 1, 20 x 25 x 1 and 24 x 25 x 1, as listed in the Trane source document's filter table. Which size fits depends on your cabinet and return. This page is pending human review, so check the source excerpt below. 16 x 25 x 1; 20 x 25 x 1; 24 x 25 x 1.

How often should I replace the Trane S9X1 / S9X2 / S9B1 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.

How thick is the Trane S9X1 / S9X2 / S9B1 filter?

Every size found in the source table is 1 in. thick: 16 x 25 x 1, 20 x 25 x 1 and 24 x 25 x 1. Pending human review; check the excerpt.

Where does this information come from?

Manufacturer document for Trane S9X1 / S9X2 / S9B1 (https://elibrary.tranetechnologies.com/public/residential-hvac/Literature/Installation%20Operation%20and%20Maintenance/FNR-SVX002B-EN_08292026.pdf), last checked 2026-11-04.