HVAC Decoder
Lennox Tonnage From Model Number
Where Lennox puts the capacity code, what each code means, and the readings that look like capacity but are not. Read out of 2 documents Lennox publishes itself, named further down with the date each was fetched.
Starting the decoder. The capacity tables below this box are already loaded, so you can read your code off them now.
Nominal capacity from a model number is a nameplate convention, not a measurement. Actual delivered capacity depends on the matched indoor unit, line set, airflow and conditions. Confirm against the data plate's BTU/h rating and the AHRI certificate for the matched system.
Lennox Capacity Codes and Tonnage
Current R-454B generation
Capacity sits at the first dash group. The group after it is the VOLTAGE (230, 233, 463), never a second capacity. Example: SL25KCV-036-230A-1.
| Code | Nominal BTU/h | Tons | Code / 12 |
|---|---|---|---|
| 018 | 18,000 | 1.5 | same answer |
| 024 | 24,000 | 2 | same answer |
| 030 | 30,000 | 2.5 | same answer |
| 036 | 36,000 | 3 | same answer |
| 041 | 42,000 | 3.5 | 3.42, so the division is wrong here |
| 042 | 42,000 | 3.5 | same answer |
| 047 | 48,000 | 4 | 3.92, so the division is wrong here |
| 048 | 48,000 | 4 | same answer |
| 059 | 60,000 | 5 | 4.92, so the division is wrong here |
| 060 | 60,000 | 5 | same answer |
Table transcribed from MODEL NUMBER IDENTIFICATION (Current Product) (Form 210965, March 2025), fetched from lennox.com on 2026-07-24.
The Lennox codes that dividing by 12 gets wrong
The usual shortcut is that a capacity code is the nominal BTU/h divided by 1,000, so dividing it by 12 gives the tonnage. Lennox prints 3 codes where that arithmetic disagrees with Lennox's own table, and the table is what the equipment is sold against:
| Code | Lennox prints | Code / 12 gives |
|---|---|---|
| 041 | 3.5 tons | 3.42 |
| 047 | 4 tons | 3.92 |
| 059 | 5 tons | 4.92 |
These are not derivable, only transcribable, which is why this decoder carries Lennox's printed table rather than a formula. If you meet one of these codes in the field, arithmetic will land you between two real sizes, and the printed table is the only thing that resolves it.
Worked example: Lennox SL25KCV-036-230A-1
Capacity code 036 at characters 9-11 of SL25KCV-036-230A-1: 36,000 BTU/h, which is 3 tons at 12,000 BTU/h per ton. The dash group between the series and the voltage is the nominal cooling capacity in Lennox's current-product model scheme; Lennox prints an explicit code table including the odd codes 041, 047 and 059.
- Refrigerant: R-454B. The K after the efficiency digits is Lennox's refrigerant position (K = R-454B) in the current-product scheme.
- Product tier: Dave Lennox Signature Collection. Leading letters SL (SL = Dave Lennox Signature Collection, EL = Elite, ML = Merit).
- Product type: Air conditioner. Unit type C (C = air conditioner, P = heat pump, L = cold climate heat pump, SL = cold climate heat pump side discharge).
- Efficiency: Nominal efficiency 25. Digits 25 sit in the position Lennox labels "Nominal Efficiency". Lennox does not print SEER or SEER2 against this position, so neither is claimed here.
- Stage: Variable-capacity compressor. Compressor stage character V (1 = single, 2 = two-stage, V = variable capacity).
- Power supply: 208/230V, 1 phase, 60Hz. The group after the capacity is the voltage code, NOT capacity: 230.
What is specific to Lennox
Models this decoder refuses rather than guesses
An undocumented code publishes nothing. Each of these would produce a plausible number by general arithmetic, and the decoder returns no match instead, because no Lennox document supports it.
| Model | What the decoder returns | Why |
|---|---|---|
| SL25KCV-055-230A-1 | no match | 055 is absent from the Nominal Cooling Capacity table in Form 210965, so no tonnage is published for it. |
The Lennox documents behind this page
Fetched from lennox.com on 2026-07-24. Covers the current generation: the Nominal Cooling Capacity table plus the tier, refrigerant, unit-type and compressor-stage positions.
Fetched from lennox.com on 2026-07-24. Covers the general dash-group rule in Lennox's own words, that the numerals following the dash indicate thousands of Btuh capacity, worked through HS26-060-1P and GCS16-090-350-2Y.
Frequently asked questions
How do I find the tonnage of a Lennox unit from the model number?
Read the capacity code: on Lennox it sits at the first dash group. The group after it is the VOLTAGE (230, 233, 463), never a second capacity. On SL25KCV-036-230A-1 that code is 036, which is 36,000 BTU/h, or 3 tons, because one ton of cooling is 12,000 BTU/h. Use the OUTDOOR unit's model number for system cooling capacity; the indoor air handler or coil carries its own number. This position comes from Lennox's own Form 210965, not from a third-party chart.
Can I just divide the Lennox capacity code by 12?
Not on every code. Lennox prints 3 capacity codes where that division gives the wrong answer: 041 is 3.5 tons where dividing gives 3.42, 047 is 4 tons where dividing gives 3.92, 059 is 5 tons where dividing gives 4.92. Those values come from Lennox's own printed table rather than from arithmetic, which is the whole reason the table exists. On every other code in the table the division does work.
Where is the model number on a Lennox unit?
On the unit nameplate on the outdoor cabinet, where Lennox prints the model as dash-separated group. It is labeled M/N, MODEL or MODEL NO., usually printed directly above or beside the serial number. The model number describes what the unit is, including its capacity. The serial number describes when it was built and carries no capacity information at all.
Which Lennox document is this based on?
MODEL NUMBER IDENTIFICATION (Current Product) (Form 210965, March 2025), fetched from lennox.com on 2026-07-24, which covers the current generation: the Nominal Cooling Capacity table plus the tier, refrigerant, unit-type and compressor-stage positions. Model Numbering Systems (Model Numbering Systems, section 3.1), fetched from lennox.com on 2026-07-24, which covers the general dash-group rule in Lennox's own words, that the numerals following the dash indicate thousands of Btuh capacity, worked through HS26-060-1P and GCS16-090-350-2Y. Every capacity value on this page traces to one of those documents, and each is named with the date it was fetched so you can pull it yourself.
Is the decoded tonnage the size I should install?
No. Nominal tonnage is what the unit was built to deliver, not what the building needs, and the old unit may have been oversized or sized before insulation and window changes. Treat it as a starting clue and run a load calculation before matching a replacement. Actual delivered capacity also depends on the matched indoor unit, line set, airflow and conditions.
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Other brands with their own manufacturer nomenclature document: Carrier tonnage by model number, Trane tonnage by model number, Goodman tonnage by model number, Amana tonnage by model number.
Got the tonnage? Check it against the actual load.
The old unit's nominal size is a clue, not a load calculation. Oversized systems short-cycle and dehumidify poorly. Run the numbers before you match a replacement.