HVAC Size Calculator
Enter your home's conditioned area and climate zone to estimate the BTU and tonnage you need. This is a Manual J approximation.
What your result means
This multiplies your square footage by a BTU-per-square-foot factor for the climate, then converts to tons at 12,000 BTU per ton. It's a rough Manual J approximation that ignores insulation, windows, orientation, and air leakage. Don't buy equipment off it: oversized systems short-cycle and dehumidify poorly, so get a real Manual J load calc from a licensed tech.
How to use this calculator
- Measure conditioned (heated/cooled) sq ft.
- Pick climate zone (1 hot to 7 cold).
- Read BTU and tonnage needed.
- 12,000 BTU = 1 ton of AC.
- For precise sizing, hire HVAC tech for Manual J calc.
The formula
Multiply the home's square footage by a BTU-per-square-foot factor that depends on the climate zone, then divide by 12,000 for tons.
Worked example
Say you've got a 2,000 sq ft home in a mild zone (2-3), figured at 25 BTU a square foot. That's 50,000 BTU, or about 4.2 tons.
BTU per sq ft by climate zone
| Zone | BTU / sq ft |
|---|---|
| 1 - Hot | 30 |
| 2-3 - Mild | 25 |
| 4-5 - Cool | 22 |
| 6-7 - Cold | 20 |
Tips & gotchas
- This is a Manual J approximation; real sizing weighs insulation, windows, and sun exposure.
- 12,000 BTU equals 1 ton of AC.
- An oversized AC short-cycles and pulls out less humidity.
- An undersized unit struggles to keep up in extremes.
- Tax credits are often available for high-efficiency units.
Frequently asked questions
What size AC for a 2,000 sq ft house?
About 4 tons in a moderate climate. Use the calculator for an estimate.
What is Manual J?
ACCA's load calculation method, the gold standard for HVAC sizing.
Is bigger always better for HVAC?
No. Oversized units short-cycle and don't dehumidify properly.
How is BTU different from tonnage?
12,000 BTU per hour equals 1 ton of cooling.
Should I trust online HVAC calculators?
For a rough estimate, yes. Get a Manual J from a licensed tech for the actual install.
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Estimates only — see our full disclaimer.