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Our script found these filter sizes in the Lennox SLP99UHV source document's filter table: 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 / part numbers 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.
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 SLP99UHV
Last checked 2026-10-23. Manufacturers revise documents. If your unit's label disagrees, trust the label.
TABLE 1
4 - Route auxiliary drain line so that water draining from
Furnace Filter Size
this outlet will be easily noticed by the homeowner.
Cabinet Width Side Return Bottom Return
5- If necessary, run the condensate line into a
condensate pump to meet drain line slope 17-1/2” 16 X 25 X 1 (1) 16 X 25 X 1 (1)
requirements. The pump must be rated for use 21” 16 X 25 X 1 (1) 20 X 25 X 1 (1)
with condensing furnaces. Protect the condensate
discharge line from the pump to the outside to avoid 24-1/2” 16 X 25 X 1 (2) 24 X 25 X 1 (1)
freezing.
Duct System
6 -
Continue with exhaust, condensate and intake
piping installation according to instructions. Use industry-approved standards to size and install the
supply and return air duct system. This will result in a qui-
INTAKE PIPE *GAS CONNECTION et and low-static system that has uniform air distribution.
EXHAUST PIPE See below for proper duct installation.
*Gas connector may be
used for Canadian SUPPLY
AIR Install self tapping screws
to seal any potential air
able by local authority leaks
having jurisdiction.Our script found these filter sizes in the Lennox SLP99UHV source document's filter table: 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. 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 SLP99UHV (https://www.lennox.com/dA/e5e74d387e/507999-02c.pdf), last checked 2026-10-23.