AC Tonnage from the Model Number

Last updated: 2026-10-30

An air conditioner's size in tons is coded in its model number. The code is thousands of BTU per hour; a BTU (British thermal unit) is a unit of heat. So a 36 means 36,000 BTU per hour, or 3 tons. One maker, Trane, gives a rule in its 2024 guide. Find an even number between 18 and 60 in the model number, then divide it by 12. Some makers also use odd codes; the table below lists them.

Trane says “one ton corresponds to 12,000 BTUs” (12,000 BTU per hour). So a 24 is 2 tons, a 30 is 2.5 tons and a 60 is 5 tons.

Source: Trane, What is HVAC Tonnage and Why Does it Matter?

Where Each Maker Puts the Tonnage Code

Find your maker, then count letters and numbers from the left to the places shown. Each example is the maker's own.

Tonnage Code by Maker
Maker	Maker's example model number	Where the code sits	Codes and tons, as the maker prints them	Source
Carrier	24ABA336A0030000 (3 tons)	Characters 7 and 8	18 = 1-1/2, 24 = 2, 30 = 2-1/2, 36 = 3, 42 = 3-1/2, 48 = 4, 60 = 5	Carrier service manual 24-25-9SM (PDF)
Trane	5TTR5024A1000AA (2 tons)	Characters 7 and 8	12 = 1.0, 18 or 19 = 1.5, 24 or 25 = 2.0, 30 or 31 = 2.5, 36 or 37 = 3.0, 42 or 43 = 3.5, 48 or 49 = 4.0, 60 or 61 = 5.0, 72 = 6.0	Trane Product Handbook 22-8301-39 (PDF)
Goodman	GLXS4BA3610AA (3 tons)	Characters 8 and 9	18 = 1½, 24 = 2, 30 = 30,000 BTU/h (see note), 36 = 3, 42 = 3½, 48 = 4, 60 = 5	Goodman SS-GLXS4B-R32 (PDF)
Lennox	SL25KCV-036-230A-1 (3 tons)	The three digits after the first dash	018 = 1.5, 024 = 2, 030 = 2.5, 036 = 3, 041 or 042 = 3.5, 047 or 048 = 4, 059 or 060 = 5	Lennox Model Number Identification (PDF)

Goodman's model-number key prints the 30 code as “2 Tons”. Its spec table on the next page rates the 30 unit at a nominal (rated) cooling of 30,000 BTU/h, or BTU per hour. That is 2.5 tons at 12,000 BTU per ton. Lennox's 041, 047 and 059 codes divide to 3.4, 3.9 and 4.9, but Lennox lists them as 3.5, 4 and 5 tons. Lennox lists these codes for its air conditioners and heat pumps that use R-454B refrigerant. Refrigerant is the coolant that carries heat through the unit's lines. A heat pump is a unit that both cools and heats.

Reading your Own Model Number

Find the rating plate, the maker's label on the outdoor unit. Trane says it is “usually located on the side or back of the unit.”
Copy the model number, not the serial number.
Find your maker in the table and read the characters it names. If your maker is not listed, look for one of 18, 24, 30, 36, 42, 48 or 60 in the model number.
Divide that number by 12 for tons: 42 ÷ 12 = 3.5 tons.

The serial number on the same rating plate gives the build date: read it with our date code pages.

Source: Trane, What is HVAC Tonnage and Why Does it Matter?

Sources

Trane, What is HVAC Tonnage and Why Does it Matter? (published 2024-02-27, updated 2026-06-22): https://www.trane.com/residential/en/resources/glossary/what-does-ton-mean-in-hvac/, accessed 2026-10-30
Carrier, Residential Air Conditioners and Heat Pumps Using R-22 and Puron® Refrigerant: Application Guideline and Service Manual, catalog no. 24-25-9SM, edition date 09/19 (PDF), “Air Conditioner and Heat Pump Model Number Nomenclature”, page 3: https://www.shareddocs.com/hvac/docs/1009/Public/03/24-25-9SM.pdf, accessed 2026-10-28
Trane, Product Handbook, Residential & Light Commercial, 22-8301-39, effective 1/1/26 (PDF), “Model Nomenclature Residential – Outdoor”, page NOM-1: https://elibrary.tranetechnologies.com/public/residential-hvac/Literature/Product%20Catalog/22-8301-39_05012026.pdf, accessed 2026-10-28
Goodman, GLXS4B R-32 split system air conditioner specification sheet SS-GLXS4B-R32 (06/24, PDF), nomenclature, page 2, and product specifications, page 3: https://mobile.goodmanmfg.com/mobileapp/stellent/pdf/infoPdf/Lit/SS-GLXS4B-R32.pdf, accessed 2026-10-30
Lennox, Model Number Identification, form 210965 (March 2025, PDF), page 2: https://www.lennox.com/dA/d1bf319d00/, accessed 2026-10-30