Calculators
HVAC Load Calculator
Estimate the cooling or heating load in BTU per hour and air conditioner tonnage from area, climate, insulation and occupancy.
- Runs in your browser
- Nothing uploaded
The tool
Enter your numbers below. Results update as you type, and nothing leaves your browser.
Everything you enter stays on your own machine. Nothing is sent to us or to anyone else, which you can confirm in your browser network tab.
What people use it for
- Sanity-checking an installer's proposed size
- Sizing a mini-split for one room
- Planning an extension
- Comparing equipment quotes
About this tool
What the HVAC Load Calculator does
HVAC equipment should match the home’s heat gain and loss. A full Manual J calculation is the professional standard; this rule-of-thumb estimate starts from BTU per square foot for your climate and adjusts for ceiling height, insulation, sun exposure, occupants and kitchens. One ton of cooling equals 12,000 BTU per hour.
Formula
- Base = area × climate factor
- Adjust for ceiling height (× height ÷ 8), insulation and sun (+10%)
- Add 600 BTU per occupant above two and 4,000 BTU for a kitchen
- Tons = BTU ÷ 12,000
Worked example
Using the starting values in the calculator above:
| Input | Value |
|---|---|
| Conditioned area | 1,800 sq ft |
| Climate | Moderate (25 BTU/sq ft) |
| Ceiling height | 8 ft |
| Insulation and windows | Average |
| Mostly sunny exposure | No |
| Occupants | 4 |
| Includes kitchen | Yes |
| Result | Value |
|---|---|
| Estimated load | 50,200 |
| Cooling tons | 4.18 |
| Nearest half-ton size up | 4.5 ton |
| In kilowatts | 14.7 |
How to read the result
Oversized air conditioners short-cycle, dehumidify poorly and wear faster. Bigger is not better.
Ask installers for a Manual J load calculation; it accounts for orientation, windows, ducts and local design temperatures.
For planning only. Electrical, gas and refrigerant work must follow current codes and be carried out or checked by a licensed professional.
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Questions
Questions about this tool
The things clients actually want to know — costs, timelines, ownership and what happens after launch.
Rules of thumb range from about 20 to 35 BTU per square foot depending on climate and insulation.
Often around 3 to 4 tons in moderate climates, but a Manual J calculation gives the right answer.
12,000 BTU per hour.
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