HVAC Tonnage Calculator (AC Size by Room Area)
Enter area and climate to estimate cooling BTU and AC tons.
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HVAC Tonnage Calculator (AC Size by Room Area) by TheCalcTools
How the HVAC Tonnage Calculator (AC Size by Room Area) works
Cooling load starts from area × a climate-based BTU per square foot.
It is adjusted for ceiling height (relative to 8 ft), insulation and sun exposure, then adds 600 BTU per person above two and 4,000 BTU for a kitchen.
One ton of cooling is 12,000 BTU per hour. Round to the nearest half ton.
The formula
Worked example
Using the default values shown in the calculator:
| Area to cool (sq ft) | 1500 |
|---|---|
| Climate | Moderate (25 BTU per sq ft) |
| Ceiling height (ft) | 8 |
| Insulation | Average |
| Sun exposure | Average |
| People regularly in the space | 4 |
| Kitchen included | 0 |
- 1,500 sq ft × 25 BTU = 37,500 BTU, plus 1,200 for the extra 2 people = 38,700 BTU per hour.
- That is 3.23 tons, so a 3.0 ton unit is the nearest standard size.
Result:
| Cooling needed (BTU per hour) | 38,700 |
|---|---|
| Tons (12,000 BTU per ton) | 3.23 |
| Nearest standard AC size (tons) | 3.0 |
| Cooling capacity (kW) | 11.3 |
| Square feet per ton | 465 |
Frequently asked questions
Is this a Manual J calculation?
No. It is a rule-of-thumb estimate. A proper Manual J load calculation by a contractor accounts for windows, orientation, ducts and local weather. Do not oversize, because an AC that is too big cycles on and off and removes less humidity.
How many square feet does a 3-ton AC cool?
Roughly 1,500 to 2,000 sq ft, depending on climate and insulation.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.