Pool Heat Pump Size Calculator
From the spec sheet; 5 is typical.
US average $0.18/kWh (EIA).
Recommended heat pump (output)
100k BTU/h
This pool needs about 81,600 BTU/h of heat output to hold 17 °F above the air; a 100,000 BTU/h heat pump covers it.
- Required output
- 81,600 BTU/h (23.9 kW)
- Electrical draw
- 5.86 kW at COP 5
- Running cost
- $1.07 per hour at full output
- First heat-up
- 15 hours, about $16.01 (before heat losses)
How it's calculated
- The surface-area rule with the factor 12 is the U.S. Department of Energy's pool heater sizing formula (1–1.25 °F/h rise, 3.5 mph wind). DOE recommends a professional sizing analysis for a final choice.
- Standard sizes come from DOE's Energy Saver guide: 75k, 100k, 125k BTU/h. Above that, the calculator suggests two units.
- COP 5 is the example DOE uses. 3,412 BTU = 1 kWh. Electricity defaults to $0.18/kWh (U.S. Energy Information Administration, Short-Term Energy Outlook, us average residential electricity price (2026 forecast)).
Worked example
A 15,000 gallon pool with 400 sq ft of surface, wanted at 82 °F, coolest swim month averaging 65 °F, water now at 70 °F:
- Required output: 400 × (82 − 65) × 12 = 81,600 BTU/h → standard size 100,000 BTU/h.
- Electrical draw: 100,000 ÷ (5 × 3,412) = 5.86 kW → $1.07 per hour.
- First heat-up: 15,000 × 8.34 × 12 = 1,501,200 BTU ÷ 100,000 = 15 hours, about $16.01.
Compare that with a gas heater using the heater size calculator: gas heats faster, while a heat pump delivers the same heat for less money when the air is mild.
Heat pump size by pool and climate
Target 82 °F; "air" is the average air temperature of your coolest swim month.
| Pool | Air 75 °F | Air 70 °F | Air 65 °F |
|---|---|---|---|
| 12 × 24 ft | 75k | 75k | 75k |
| 15 × 30 ft | 75k | 75k | 100k |
| 16 × 32 ft | 75k | 75k | 125k |
| 18 × 36 ft | 75k | 100k | 2 × 125k |
BTU/h output; k = thousand. U.S. Department of Energy, Energy Saver: Heat Pump Swimming Pool Heaters (standard sizes and COP example).
Frequently asked questions
What size heat pump do I need for my pool?
Multiply the surface area by the difference between the water temperature you want and the average air temperature of your coolest swim month, then by 12. A 400 sq ft pool at 82 °F with 65 °F air needs about 81,600 BTU/h, so a 100,000 BTU/h heat pump.
How much does it cost to run a pool heat pump?
A 100,000 BTU/h heat pump at COP 5 draws about 5.9 kW, roughly $1.07 per hour at the US average of $0.18 per kWh. Heat pumps cycle off once the pool is at temperature, so daily cost depends on how much heat the pool loses.
How long does a heat pump take to heat a pool?
Much longer than a gas heater. Warming 15,000 gallons by 12 °F with a 100k BTU/h heat pump takes about 15 hours of run time before losses, often two to four days in practice. Keep it running and use a cover to hold the heat.
Do heat pumps work in cold weather?
They work, but capacity and efficiency fall as the air cools, and most units struggle below about 50 °F. They are best for extending the swim season in mild weather; for heating in cold weather a gas heater is faster.
What does COP mean for a pool heat pump?
Coefficient of performance: units of heat delivered per unit of electricity used. A COP of 5 means 5 kWh of heat for every 1 kWh of electricity. COP is measured at standard test conditions and is higher in warm, humid air.
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