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Lennox furnace error codes

170 codes with causes and test steps, plus 5 settings tables.

Settings and specs

Recommended filter size by cabinet width

Filters · EL296UHV

Cabinet width	Side return	Bottom return
17-1/2 in.	16 x 25 x 1 in. (1)	16 x 25 x 1 in. (1)
21 in.	16 x 25 x 1 in. (1)	20 x 25 x 1 in. (1)
24-1/2 in.	16 x 25 x 1 in. (2)	24 x 25 x 1 in. (1)

• Number in brackets is the quantity of filters.
• Filters are field supplied and installed outside the furnace; inspect monthly.
• High-efficiency filters add static pressure; size them so total static stays within limits.
• On 090XV60C, 110XV60C and 135XV60D single side return, high airflows need the return air base and a transition to a 20 x 25 x 1 in. filter.

Source: Lennox EL296UHV(X) Unit Information, Corp 1125-L5 (rev. 03/2022), Table 34 filter sizes, p.88 (printed p.87); blower data notes p.18-26

Recommended filter size by cabinet width

Filters · Lennox SL280UHV

Cabinet width	Side return	Bottom return
14-1/2 in.	16 x 25 x 1 in. (1)	14 x 25 x 1 in. (1)
17-1/2 in.	16 x 25 x 1 in. (1)	16 x 25 x 1 in. (1)
21 in.	16 x 25 x 1 in. (1)	20 x 25 x 1 in. (1)
24-1/2 in.	16 x 25 x 1 in. (2)	24 x 25 x 1 in. (1)

• Number in brackets is filter quantity; filters are field supplied.
• Never run the unit without a filter installed.
• 60C/60D sizes needing over 1800 cfm: use bottom return, both sides, bottom + one side, or single side with return air base and 20 x 25 x 1 in. filter.
• Cabinet A width: 070V36A 14 in. (manual), 090V36B/090V48B 17-1/2 in., 090V60C/110V60C 21 in., 135V60D 24-1/2 in.

Source: Lennox SL280UHV Installation Instructions 508245-01 (04/2024), Table 1 p.12; Unit Dimensions p.2

Filter sizes by cabinet width

Filters · Lennox ML180UHE

Cabinet	Side return	Bottom return
A - 14-1/2 in.	16 x 25 x 1 (1)	14 x 25 x 1 (1)
B - 17-1/2 in.	16 x 25 x 1 (1)	16 x 25 x 1 (1)
C - 21 in.	16 x 25 x 1 (1)	20 x 25 x 1 (1)
D - 24-1/2 in.	16 x 25 x 1 (2)	24 x 25 x 1 (1)

• Filters are field supplied; check monthly.
• Cabinet letter is the letter after the cooling size in the model number: A = 045E36AK, 070E36AK; B = 070E36BK, 090E48BK; C = 090E60CK, 110E60CK; D = 135E60DK.

Source: Lennox ML180UHEK Unit Information 100161/100166, Table 16, p.30

Filter sizes (filter rack kits)

Filters · Lennox EL195UHNE

Cabinet	Horizontal end rack	Side return rack
B width (040, 060)	18 x 25 x 1 (kit 87L96)	16 x 25 x 1 (kit 44J22)
C width (080, 100)	20 x 25 x 1 (kit 87L97)	16 x 25 x 1 (kit 44J22)

• Filters are field supplied; check monthly.
• 100NE60C over 1800 cfm with single side return needs a 20 x 25 x 1 filter via return air base and transition.

Source: Lennox EL195UHNE Unit Information Corp 1801-L1 (rev 04/2024), Optional Accessories, p.3

Filter sizes by cabinet width

Filters · Lennox SL297NV

Cabinet	Side return	Bottom return
17-1/2 in. (040, 060)	16 x 25 x 1 (1)	16 x 25 x 1 (1)
21 in. (080)	16 x 25 x 1 (1)	20 x 25 x 1 (1)

• No filter or rack supplied; use a field high-velocity rated filter and keep one in place whenever the unit runs.

Source: Lennox SL297UHNV Installation Instructions 507760-02 (02/2018), Table 1, p.11

Models covered

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.