Lennox · model number decoder
Lennox Model L LGM
Lennox's ultra-high-efficiency Model L gas/electric rooftop with the CORE controller and R-454B. The 12-character model tells you size, blower, gas heat, revision and voltage.
Gas heat / electric cooling packaged rooftop · 3–25 tons · R-454B
Model numbers starting LGM.
Quick answers
- Tonnage from the model number
LGM240U5MS2Yis a 20-ton unit: characters 4–6,240, are the nominal size.036= 3 tons048= 4 tons060= 5 tons074= 6 tons092= 7.5 tons102= 8.5 tons120= 10 tons150= 12.5 tons156= 13 tons180= 15 tons210= 17.5 tons240= 20 tons300= 25 tonsSource: Form 211134, page 1; Form 211135, page 1; Form 211136, page 1.
- Factory filters by tonnage
3–6 tons (4) 20 x 20 x 2 in. 7.5–12.5 tons (4) 20 x 25 x 2 in. 13–25 tons (6) 24 x 24 x 2 in. Source: Form 211134, page 22; Form 211135, page 22; Form 211136, pages 29, 30, 31. Check the rack before ordering; filters get changed over the years.
- Age from the serial number
Characters 3–4 are the year and character 5 is the month letter (A = January through M = December, skipping I).
5178M99989was built in December 1978. How to read itSource: Lennox 3.1 Model Numbering Systems, page 3.
Sizes and filter sizes
| Size code | Nominal tons | Return-air filters |
|---|---|---|
| 036 | 3 | (4) 20 x 20 x 2 in. |
| 048 | 4 | (4) 20 x 20 x 2 in. |
| 060 | 5 | (4) 20 x 20 x 2 in. |
| 074 | 6 | (4) 20 x 20 x 2 in. |
| 092 | 7.5 | (4) 20 x 25 x 2 in. |
| 102 | 8.5 | (4) 20 x 25 x 2 in. |
| 120 | 10 | (4) 20 x 25 x 2 in. |
| 150 | 12.5 | (4) 20 x 25 x 2 in. |
| 156 | 13 | (6) 24 x 24 x 2 in. |
| 180 | 15 | (6) 24 x 24 x 2 in. |
| 210 | 17.5 | (6) 24 x 24 x 2 in. |
| 240 | 20 | (6) 24 x 24 x 2 in. |
| 300 | 25 | (6) 24 x 24 x 2 in. |
Source: Form 211134, pages 1, 22; Form 211135, pages 1, 22; Form 211136, pages 1, 29, 30, 31. Factory filter sizes. Check the rack before ordering; filters get changed over the years.
Lennox Model L LGM model number nomenclature
Example: LGM240U5MS2Y. Select a position to jump to its codes.
Position 1 Brand
| L | Lennox |
|---|
Form 211136, page 1
Position 2 Unit type
| G | Gas heat with electric cooling |
|---|
Form 211136, page 1
Position 3 Family
| M | Model L series |
|---|
Form 211136, page 1
Position 4–6 Nominal cooling capacity
| 036 | 3 tons |
|---|---|
| 048 | 4 tons |
| 060 | 5 tons |
| 074 | 6 tons |
| 092 | 7.5 tons |
| 102 | 8.5 tons |
| 120 | 10 tons |
| 150 | 12.5 tons |
| 156 | 13 tons |
| 180 | 15 tons |
| 210 | 17.5 tons |
| 240 | 20 tons |
| 300 | 25 tons |
Form 211134, page 1; Form 211135, page 1; Form 211136, page 1
Position 7 Cooling efficiency
| U | Ultra-high efficiency |
|---|
Form 211136, page 1
Position 8 Refrigerant
| 5 | R-454B |
|---|
Form 211136, page 1
Position 9 Blower type
| E | Single-zone VAV, DirectPlus direct-drive blower (3–12.5 tons) |
|---|---|
| P | VAV, DirectPlus direct-drive blower (3–12.5 tons) |
| M | Single-zone VAV, belt drive (13–25 tons) |
| V | VAV, belt drive (13–25 tons) |
Form 211134, page 1; Form 211136, page 1
Position 10 Heating type
| B | Standard gas heat, 2 stage, low NOx (3–6 tons) |
|---|---|
| Q | Medium gas heat, 2 stage, low NOx (3–6 tons) |
| X | High gas heat, 2 stage, low NOx (3–6 tons) |
| L | Low gas heat, 1 stage (13–25 tons) |
| S | Standard gas heat, 2 stage (7.5–25 tons) |
| M | Medium gas heat, 2 stage (7.5–25 tons) |
| H | High gas heat, 2 stage (7.5–25 tons) |
| P | Standard gas heat, modulating (7.5–25 tons) |
| K | Medium gas heat, modulating (7.5–25 tons) |
| R | High gas heat, modulating (7.5–25 tons) |
Form 211134, page 1; Form 211136, page 1
Position 11 Minor design sequence
| 1 | 1st revision (listed for 3–6 tons) |
|---|---|
| 2 | 2nd revision (listed for 13–25 tons) |
| 3 | 3rd revision (listed for 7.5–12.5 tons) |
Form 211134, page 1; Form 211136, page 1; Form 211135, page 1
Position 12 Voltage
| Y | 208/230 V, three phase, 60 Hz |
|---|---|
| G | 460 V, three phase, 60 Hz |
| J | 575 V, three phase, 60 Hz |
Form 211136, page 1
How old is this unit? Reading a Lennox serial number
A two-digit plant code, a two-digit year, a month letter, then a five- or six-digit sequence number. Lennox’s own example 5178M 99989 came from plant 51 in December 1978.
Example: 5178M99989
- Scope: One serial numbering system across Lennox products
- Positions 1–2: Plant (location) code, e.g. 56 = Stuttgart, Arkansas
- Positions 3–4: Year (21 = 2021)
- Position 5: Month letter: A = January, B = February, C = March … M = December (no I)
- Positions 6 onward: Five- or six-digit unique number
Source: Lennox 3.1 Model Numbering Systems, pages 1, 3; Lennox EHB model ID, R-454B and R-32, page 9. This is the manufacture date, not the install date.
- Lennox’s commercial rooftop handbooks don’t explain the serial. Its current table is in the residential model ID handbook and lists only January to March; its all-products numbering guide shows the same layout in a diagram with every month, A to M without I. We use that month list.
- Plant codes have changed over the years, so we date the unit but don’t name the plant.
Notes and limits
- Covers R-454B Model L LGM gas/electric units (refrigerant character 5) from 3 to 25 tons. Earlier R-410A Model L units and the LCM electric/electric units are not decoded here; LCM uses L for 60 kW electric heat, which means low gas heat on an LGM.
- Blower and heat codes depend on the cabinet: E and P blowers are 3–12.5 tons, M and V are 13–25 tons; B, Q and X heat codes are 3–6 tons only.
- Lennox prints one minor design sequence per cabinet in these sheets (1 for 3–6 tons, 3 for 7.5–12.5 tons, 2 for 13–25 tons). A different digit on a nameplate means a revision these sheets do not describe.
- Filter sizes are the factory MERV 4 return-air filters from the specification tables. Confirm against the rack in the unit.
- No serial-number date decoder: no Lennox-owned document found states the commercial rooftop serial format.
Keep the model and serial with the unit
BoltWright keeps every rooftop’s model, serial, history and open findings with the building, so the next tech starts with what the last one knew. Capture works without reception.
See BoltWright →Not the one who picks the software? Send it to whoever runs the shop.
BoltWright put this page together from the manufacturer’s published documents, and we aren’t affiliated with Lennox. Check the unit’s nameplate and the current Lennox literature before you order parts.
← All rooftop families