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Our script found these filter sizes in the Lennox SL280UHV source document's filter table: 14x25x1, 16x25x1, 20x25x1, 24x25x1. This page is pending human review, so check the source excerpt on the page to see which size applies to your cabinet and return.
Auto-extracted · review pending Filter sizes auto-extracted from the manufacturer document.
| Sizes found in the source table |
|---|
| 14 x 25 x 1 |
| 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.
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.
Manufacturer document for Lennox SL280UHV
Last checked 2026-10-25. Manufacturers revise documents. If your unit's label disagrees, trust the label.
This unit is not equipped with a filter or rack. A field-pro- nace is operating and it must not allow leaks. In horizontal
vided high-velocity filter is required for the unit to operate units, install self tapping screws in the three evaporator
properly. TABLE 1 lists recommended filter sizes. coil screw holes made for upflow applications to seal the
A filter must be in place any time the unit is operating. top cap to the vestibule panel.
TABLE 1 Return Air Plenum
NOTE - Return air must not be drawn from a room
Furnace Cabinet Filter Size
where this furnace, or any other gas-fueled appliance
Width Side Return Bottom Return (i.e., water heater), or carbon monoxide- producing
14-1/2” 16 X 25 X 1 (1) 14 X 25 X 1 (1) device (i.e., wood fireplace) is installed.
17-1/2” 16 X 25 X 1 (1) 16 X 25 X 1 (1) When return air is drawn from a room, a negative pressure
is created in the room. If a gas appliance is operating in
21” 16 X 25 X 1 (1) 20 X 25 X 1 (1) a room with negative pressure, the flue products can be
24-1/2” 16 X 25 X 1 (2) 24 X 25 X 1 (1) pulled back down the vent pipe and into the room.
Page 12
This reverse flow of the flue gas may result in incomplete 2-
Use tin snips to cut preferred opening on the
combustion and the formation of carbon monoxide gas. cabine for repositioning the flue outlet. Use the cut
This toxic gas might then be distributed throughout the out piece as a cover plate to patch unused opening
house by the furnace duct system. on cabinet.
In upflow applications, the return air can be brought in UPFlow Position
through the bottom or either side of Our script found these filter sizes in the Lennox SL280UHV source document's filter table: 14x25x1, 16x25x1, 20x25x1, 24x25x1. This page is pending human review, so check the source excerpt on the page to see which size applies to your cabinet and return. 14 x 25 x 1; 16 x 25 x 1; 20 x 25 x 1; 24 x 25 x 1.
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.
Manufacturer document for Lennox SL280UHV (https://www.lennox.com/dA/0891b8032a/508245-01b.pdf), last checked 2026-10-25.