How to Find AC Tonnage from the Model Number
When there's no capacity printed on the data plate, the model number almost always has it. The trick is knowing what to look for.
The capacity code
Residential systems come in half-ton steps, and the model number usually includes the capacity in thousands of BTU/h:
| Code in model number | BTU/h | Tons |
|---|---|---|
| 18 | 18,000 | 1.5 |
| 24 | 24,000 | 2 |
| 30 | 30,000 | 2.5 |
| 36 | 36,000 | 3 |
| 42 | 42,000 | 3.5 |
| 48 | 48,000 | 4 |
| 60 | 60,000 | 5 |
Tons = code ÷ 12. Some brands use three digits (like 024 or 036) and some put the number in the middle of the model string.
Examples of where it shows up
- A Goodman condenser like GSX140361 includes "036", which is 3 tons.
- A Carrier model like 24ACC636A003 includes "36" in the middle, which is 3 tons.
- A Trane model like 4TTR6048 ends in "048", which is 4 tons.
Model formats change between product lines, so treat any example as a pattern, not a rule. When in doubt, look up the model's product data or installation manual, which list nominal capacity.
Don't confuse these numbers
- SEER or SEER2 ratings (14, 15, 16…) often appear in model numbers too. 14 isn't a capacity code because it doesn't divide by 6.
- Furnace model numbers show heating input in thousands of BTU/h (like 060 = 60,000 BTU/h input) and often a blower size too. That isn't cooling tonnage.
- Nominal vs. actual capacity: a "3-ton" system delivers different capacity depending on the indoor coil match, airflow and conditions. Use AHRI-matched ratings for real numbers.
Matching indoor and outdoor units
Coils and air handlers carry a capacity code too, often covering a range (like 3–3.5 tons). The outdoor unit and the indoor coil should be an AHRI-listed match, not just similar sizes.
FAQ
How do I know if my AC is 3 ton?
Look for 36 (or 036) in the outdoor unit's model number. 36,000 BTU/h ÷ 12,000 = 3 tons.
Is a 2.5 ton unit 30,000 BTU?
Yes. 2.5 tons × 12,000 = 30,000 BTU/h nominal, shown as 30 or 030 in most model numbers.
Can the model number tell me the age?
Usually not. The age is coded in the serial number. See how to tell HVAC age from the serial number.
Sources
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