Lennox furnace filter sizes

Lennox (current style: ML180, EL180, SL280, ML193, ML196, EL195, EL196, ML197, EL296, ML296, SLP98)

Example: ML180UH070XE36B (also EL296UH070XV36B, SL280UH090V36BK)

• Letters 1-2 (or 3): series. ML = Merit, EL = Elite, SL/SLP = Dave Lennox Signature.
• Next digit: stages. 1 = single-stage, 2 = two-stage (e.g. EL296).
• Next two digits: efficiency class. 80 = 80% AFUE, 93/95/96/97/98 = condensing.
• Next two letters: configuration. UH = upflow/horizontal, DF = downflow.
• Next three digits: nominal input code. 030 = 30,000; 040 = 40,000; 045 = 44,000; 060 = 60,000; 070 = 66,000; 080 = 80,000; 090 = 88,000; 100 = 100,000; 110 = 110,000; 135 = 132,000 BTU/h.
• Optional N: low-NOx (14 ng/J) model (e.g. EL195UH040NE36B, SL280UH060NV36A).
• Optional X: meets California NOx standard (40 ng/J).
• Next letter: blower motor. E = constant-torque (high-efficiency) motor, V = variable speed, P = older PSC models.
• Next two digits: nominal cooling airflow class. 24 = 1.5-2 ton, 36 = 2-3 ton, 48 = 3-4 ton, 60 = 3-5 ton (approx.; see EHB).
• Next letter: cabinet width. A = 14-1/2 in., B = 17-1/2 in., C = 21 in., D = 24-1/2 in. This letter is what picks the filter-size row.
• Trailing K: refrigerant-detection (R-454B) version (2025+). Nameplate may add -01, -02 revision suffix.

Where this comes from: ML180UHE Product Specifications (EHB) bulletin 210825, July 2024, 'Model Number Identification', page 1.

How it connects to the filter: Lennox installation manuals give one table by cabinet width: side return always 16 x 25 x 1 (two of them on D/24-1/2 in.); bottom return 14 / 16 / 20 / 24 x 25 x 1 for A / B / C / D. Downflow (DF) and ML296UHV tables give one size (16 x 25 x 1) for 17-1/2 and 21 in. Filters are never shipped with the furnace.

Lennox (older G-series: G61MPV, G61MP, G51MP)

Example: G61MPV-60C-090

• G61MPV / G61MP / G51MP = family (MP = multi-position).
• First dash group: cooling class + cabinet letter (36B, 48C, 60D). Letter B = 17-1/2 in., C = 21 in., D = 24-1/2 in. (same letters as the filter table rows).
• Second dash group: nominal input code (045, 070, 090, 110, 135). G61MP spec table: 045 = 44,000, 070 = 66,000, 090 = 88,000, 110 = 110,000, 135 = 132,000 BTU/h.
• Variants such as -071, -091, -111 exist (G61MPV); trailing -1 etc. = revision.

Where this comes from: G61MP Unit Information Corp 0308-L6 (rev 10-2004) spec table; G61MPV IOM 506506-01 model list, page 2.

Not fully confirmed: Cabinet letter-to-width mapping for G-series inferred from the same Lennox convention and the filter tables (17-1/2 / 21 / 24-1/2 rows); the G-series IOMs do not print a decoder.

Related families from the same maker group

These share parts of the numbering system with Lennox, so they can help with an older or rebadged label.

Allied Air (Armstrong Air / AirEase A-prefix; Allied / Ducane 80G2, 92G1, 95G1 prefix)

Example: A80UH2E090B12 ; A95UH1E090C16S ; A96US2V110C20S ; 80G2UH090BE12 ; 95G1UH090CE16

• A-prefix: A + AFUE class (80, 92, 95, 96, 97) + configuration (UH = upflow/horizontal, US = upflow, DS/DF = downflow) + stages digit (1, 2) + motor letter (E = constant-torque ECM, V = variable speed) + input x 1000 (045, 070, 090, 110, 135) + CABINET LETTER + cooling CFM x 100 (08, 12, 16, 20) + optional suffix (S, K, etc.).
• G-prefix: AFUE class + G + stages + configuration + input code + CABINET LETTER + motor letter + cooling (e.g. 80G2UH090BE12, 95G1UH090CE16). Trailing L = variant listed in spec table.
• Cabinet letter: A = 14.5 in., B = 17.5 in., C = 21.0 in., D = 24.5 in.
• Input code: 045 = 44,000, 070 = 66,000, 090 = 88,000, 110 = 110,000, 135 = 132,000 BTU/h in the A80UH2E, A95UH1E and A96US2V tech-spec tables (92G1 spec sheet shows 135 = 135,000, so check per family).

Where this comes from: A80UH2E / 80G2UHE Service Manual 'MODEL NUMBER GUIDE' and A95UH1E/95G1UHE, A96US2V service manuals, page 2.

How it connects to the filter: Same table shape as Lennox: side 16 x 25 x 1 (two on 24.5 in.), bottom 14/16/20/24 x 25 x 1. Filters are external and field-provided.