Heat Pump Size Calculator by Climate Zone
Enter your square footage and insulation, pick your state, and see the heating capacity your house needs on a design-cold day, next to the capacity it needs for cooling.
Heat pump size
B06Scenario A
Sets the electricity rate. Pick US average if you're not sure.
From EIA for US average. Use the rate on your bill if you know it.
Rate used: 18.4¢/kWh · US average · EIA reference 2025–26 · design temp 10 °F · climate zone 4 (data as of 2026-09-26) ·
Heating capacity needed
4.0 tons of heating at 10 °F outside (US average 99% design temperature). Confirm with a Manual J load calculation before you buy.
- Design temperature difference
- 60 °F (indoor 70 °F − US average design 10 °F)
- Heat loss at design temperature
- 42,000 BTU/h
- Heating capacity with 15% margin
- 48,300 BTU/h
- Size in tons
- 4.0 tons
- Furnace input rating (÷ AFUE)
- 50,842 BTU/h
- Cooling capacity (20 BTU/sq ft × climate-zone factor)
- 40,000 BTU/h
Estimate. Formula and sources are under “How it works”. Change any input; the result updates as you type.
2026 note: The federal 25C and 25D tax credits ended for installations after Dec 31, 2025. Our numbers use 2026 rules. State rebates, HEAR/HOMES programs and utility programs may still apply.
Formula
How it works
- Design temperature difference = indoor temperature − your state's 99% winter design temperature
- Heat loss (BTU/h) = square feet × insulation factor × temperature difference (insulation factor: good 0.25, average 0.35, poor 0.50 BTU/h·°F per sq ft)
- Heating capacity = heat loss × 1.15 (a 15% margin; ACCA Manual S limits heating oversizing to 140%)
- Tons = heating capacity ÷ 12,000
- Furnace input = heating capacity ÷ AFUE
- Cooling capacity = square feet × 20 × climate factor (zone 1 1.3, zone 2 1.2, zone 3 1.1, zone 4 1.0, zone 5 0.9, zone 6 0.85, zones 7–8 0.8)
The design temperature is the outdoor temperature your area stays above 99% of the winter hours. In warm states the cooling number is bigger and sets the size; in zones 5 and colder the heating number is bigger. There are two ways to handle that: size the heat pump for cooling and add backup heat (electric strips or a furnace, "dual fuel") for the coldest hours, or size it for heating with a cold-climate model that keeps its capacity at your design temperature.
Sources: 99% design temperatures from ASHRAE Handbook of Fundamentals and ACCA Manual J table 1A (value for each state's most populous city); IECC 2021 climate zones (DOE/PNNL); envelope factors are a simplification of ACCA Manual J; 15% margin within ACCA Manual S limits; cooling rule of thumb from ENERGY STAR room sizing with a climate factor.
Worked example
A worked example
Texas uses a winter design temperature of 25 °F, so the difference is 45 °F (indoor 70 − design 25). A well-insulated 2,500 sq ft house loses 28,125 BTU/h at that temperature. With the 15% margin the heat pump needs about 32,344 BTU/h of heating, 2.7 ton. For cooling, the same house in zone 2 needs about 60,000 BTU/h, so in Texas the cooling load sets the size. Paired with a 95% furnace, the furnace input would be 34,046 BTU/h.
Reference
By state, at the default inputs
Heating capacity needed, with this page's default inputs and each state's reference prices (EIA reference 2025–26, data as of 2026-09-26).
| US average | 48,300 BTU/h | 18.4¢/kWh |
|---|---|---|
| Alabama | 40,250 BTU/h | 15.5¢/kWh |
| Alaska | 72,450 BTU/h | 25.0¢/kWh |
| Arizona | 32,200 BTU/h | 15.0¢/kWh |
| Arkansas | 44,275 BTU/h | 13.0¢/kWh |
| California | 28,175 BTU/h | 32.0¢/kWh |
| Colorado | 56,350 BTU/h | 16.0¢/kWh |
| Connecticut | 52,325 BTU/h | 30.0¢/kWh |
| Delaware | 48,300 BTU/h | 17.0¢/kWh |
| District of Columbia | 44,275 BTU/h | 19.0¢/kWh |
| Florida | 28,175 BTU/h | 15.0¢/kWh |
| Georgia | 40,250 BTU/h | 14.5¢/kWh |
| Hawaii | 8,050 BTU/h | 42.0¢/kWh |
| Idaho | 52,325 BTU/h | 12.0¢/kWh |
| Illinois | 60,375 BTU/h | 17.0¢/kWh |
| Indiana | 56,350 BTU/h | 15.5¢/kWh |
| Iowa | 64,400 BTU/h | 13.5¢/kWh |
| Kansas | 52,325 BTU/h | 14.5¢/kWh |
| Kentucky | 52,325 BTU/h | 13.0¢/kWh |
| Louisiana | 36,225 BTU/h | 12.5¢/kWh |
| Maine | 60,375 BTU/h | 26.0¢/kWh |
| Maryland | 48,300 BTU/h | 19.0¢/kWh |
| Massachusetts | 52,325 BTU/h | 29.0¢/kWh |
| Michigan | 56,350 BTU/h | 19.5¢/kWh |
| Minnesota | 68,425 BTU/h | 15.5¢/kWh |
| Mississippi | 40,250 BTU/h | 13.5¢/kWh |
| Missouri | 52,325 BTU/h | 13.0¢/kWh |
| Montana | 68,425 BTU/h | 13.0¢/kWh |
| Nebraska | 60,375 BTU/h | 12.0¢/kWh |
| Nevada | 40,250 BTU/h | 15.0¢/kWh |
| New Hampshire | 60,375 BTU/h | 27.0¢/kWh |
| New Jersey | 48,300 BTU/h | 22.0¢/kWh |
| New Mexico | 44,275 BTU/h | 15.0¢/kWh |
| New York | 48,300 BTU/h | 25.0¢/kWh |
| North Carolina | 40,250 BTU/h | 14.5¢/kWh |
| North Dakota | 72,450 BTU/h | 11.5¢/kWh |
| Ohio | 56,350 BTU/h | 16.5¢/kWh |
| Oklahoma | 48,300 BTU/h | 13.0¢/kWh |
| Oregon | 40,250 BTU/h | 14.5¢/kWh |
| Pennsylvania | 52,325 BTU/h | 18.5¢/kWh |
| Rhode Island | 52,325 BTU/h | 29.0¢/kWh |
| South Carolina | 40,250 BTU/h | 15.0¢/kWh |
| South Dakota | 68,425 BTU/h | 13.0¢/kWh |
| Tennessee | 48,300 BTU/h | 13.5¢/kWh |
| Texas | 36,225 BTU/h | 15.5¢/kWh |
| Utah | 52,325 BTU/h | 12.0¢/kWh |
| Vermont | 64,400 BTU/h | 22.0¢/kWh |
| Virginia | 44,275 BTU/h | 15.5¢/kWh |
| Washington | 40,250 BTU/h | 12.0¢/kWh |
| West Virginia | 52,325 BTU/h | 15.5¢/kWh |
| Wisconsin | 64,400 BTU/h | 17.5¢/kWh |
| Wyoming | 64,400 BTU/h | 12.5¢/kWh |
Questions
FAQ
What size heat pump for 2,000 sq ft?
At the US-average design temperature (10 °F) and average insulation: heat loss 42,000 BTU/h, 48,300 BTU/h with the margin (4.0 tons) for heating, and 40,000 BTU/h for cooling. In Illinois (design −5 °F) the heating number is 60,375 BTU/h, 5.0 tons.
Should I size for heating or cooling?
Compare the two numbers the calculator gives you. If cooling is bigger (Texas: 60,000 cooling vs 32,344 heating for 2,500 sq ft), size for cooling. If heating is much bigger (Minnesota, 1,600 sq ft, poor insulation: 78,200 heating vs 27,200 cooling), either add backup heat or choose a cold-climate model rated for your design temperature.
What is a cold-climate heat pump?
A heat pump built to keep most of its heating capacity at low outdoor temperatures. For a cold state, check the manufacturer's capacity at 5 °F against the heating number above.
Is a bigger heat pump better?
No. An oversized unit short-cycles: it turns on and off often, which wears it out and dehumidifies poorly in summer. That's why the margin is 15%, well inside the Manual S limit.
Does better insulation mean a smaller heat pump?
Yes, in direct proportion. Going from poor (0.50) to good (0.25) halves the heat loss for the same house.
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