Lennox model number tonnage
A Lennox outdoor model number reads series, size, voltage. The three digits in the middle are the size in thousands of BTU per hour. Divide by 12 for tons: EL16KC1-036-230 is 36,000 BTU/h, a 3-ton unit. Lennox gas furnaces carry the heating input right after UH or DF: EL297UH045 is the 45,000 BTU/h size.
Decode a Lennox model number
What do the size codes mean?
On an air conditioner or heat pump the code is the nominal cooling capacity in thousands of BTU per hour. One ton of cooling is 12,000 BTU/h, so the code divided by 12 is the tonnage. Some series print the code with a leading zero: 036 and 36 are the same size.
| Code | Nominal BTU/h | Tons | Variant codes in the same size class |
|---|---|---|---|
| 18 or 018 | 18,000 | 1.5 | 17, 19 |
| 24 or 024 | 24,000 | 2 | 25 |
| 30 or 030 | 30,000 | 2.5 | 31 |
| 36 or 036 | 36,000 | 3 | 37, 38 |
| 42 or 042 | 42,000 | 3.5 | 41, 43 |
| 48 or 048 | 48,000 | 4 | 47, 49 |
| 54 or 054 | 54,000 | 4.5 | |
| 60 or 060 | 60,000 | 5 | 59, 61 |
A variant code marks a slightly different version of the same size class. Not every brand uses every code.
On a gas furnace the code is the heating input in thousands of BTU per hour, always three digits: 040 is 40,000 BTU/h, 060 is 60,000, 080 is 80,000, 100 is 100,000 and 120 is 120,000. It is input, not output, and it is not tons.
Where is the tonnage in a Lennox model number?
In the examples, an asterisk stands for a character that varies from one version of the model to the next.
Lennox air conditioners and heat pumps
The three digits between the series and the voltage: SERIES-036-230.
EL16KC1-036-230 reads as 3 tons (36,000 BTU/h nominal).
Lennox’s store lists this model as a 3-ton air conditioner. No Lennox nomenclature chart was found. Lennox’s own parts and equipment store lists the cooling capacity for each model number, and certified ratings agree. Checked on October 5, 2026: 134 of 134 models in the DOE certification database and 48 of 48 in the ENERGY STAR list read to the certified size.
Where is the size in a Lennox furnace model number?
Lennox gas furnaces (EL, ML, SL and SLP series)
The three digits right after UH or DF.
EL297UH045XV36B reads as 45,000 BTU/h input.
Lennox’s store lists it as a 44,000 BTU furnace with a 3-ton blower. The two digits later in the number (36, 48, 60) are the blower size: 3, 4 or 5 tons of cooling airflow. They are not heating capacity.
No Lennox nomenclature chart was found. Lennox’s own store prints the input and blower size for each model number, and the input each model is certified at agrees. Checked on October 5, 2026: 256 of 256 models in the DOE certification database read to the certified size.
Is the size in the model number the exact capacity?
No. The code is the nominal size, the round number the unit is sold as. The capacity an air conditioner or heat pump is certified at depends on the indoor coil or air handler it is matched with, and it is usually a little below the nominal figure.
For example, the DOE certification database lists the Lennox EL18XCVS036-230A** at 30,400 to 35,400 BTU/h of cooling across the indoor units it is certified with. Its size code is 036: 3 tons, or 36,000 BTU/h nominal.
The size of the unit you have is also not proof of the size the house needs. To check it, use the AC tonnage calculator or the furnace size calculator.
Where is the model number on the unit?
The model number is on the rating plate, next to the serial number.
On a furnace, remove the top front service panel and look on the left side of the cabinet interior or on top of the blower deck.
On cooling equipment the model and serial numbers are on a nameplate or sticker near the service panel: a white label with black letters.
Model numbers this page does not read
- Packaged units (LRP and similar), ductless units (MLA, MLB, MHA) and coils: they use other layouts.
- Older Lennox numbering such as the HS, HP and G series: not checked.
- Three-phase and commercial units whose number does not end in 230.
When a model number does not match a layout, the decoder says so. It does not guess.
How old is the unit?
The serial number on the same plate holds the build date: Lennox serial number decoder.
Questions and answers
How do I tell the tonnage of a Lennox unit from the model number?
Read the three digits between the series and the voltage and divide by 12. In XC21-036-230 they are 036: 36,000 BTU/h, 3 tons.
What do Lennox codes like 041, 047 and 059 mean?
They are variants of the neighboring round sizes. Lennox’s own store lists 041 models as 3.5 tons, 047 as 4 tons and 059 as 5 tons.
What does the 36, 48 or 60 in a Lennox furnace model number mean?
It is the blower size, written as 3, 4 or 5 tons of cooling airflow. The heating input is the three-digit number right after UH or DF.
Sources
- LennoxPros store: single-phase air conditioners, model numbers with cooling capacity (manufacturer): https://www.lennoxpros.com/hvac/air-conditioners/1-phase-air-conditioners/c/r102
- US Department of Energy compliance certification database: central air conditioners and heat pumps (certified cooling capacity for each outdoor model number) (government data): https://www.regulations.doe.gov/certification-data/CCMS-4-Air_Conditioners_and_Heat_Pumps_-_Central.html
- ENERGY STAR certified air-source heat pumps (certified cooling capacity for each outdoor model number) (government data): https://data.energystar.gov/Active-Specifications/ENERGY-STAR-Certified-Air-Source-Heat-Pumps/w7cv-9xjt
- LennoxPros store: gas furnaces, model numbers with input and blower size (manufacturer): https://www.lennoxpros.com/hvac/furnaces/gas-furnaces/c/r109
- US Department of Energy compliance certification database: furnaces (certified input capacity for each model number) (government data): https://www.regulations.doe.gov/certification-data/CCMS-4-Furnaces.html
Layouts last checked against these sources on October 5, 2026. Found a model number that reads wrong? Send a correction. How layouts are verified: method and sources.