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Pool Heat Pump Size Calculator
Quick answer: A common planning rule sizes a pool heat pump at surface area × (target water temperature minus average air temperature in your coolest swim month) × about 12 BTU/h, more if windy and less with a nightly cover. Then check the model's output at that air temperature, because heat pump capacity drops as air cools.
How it works
Pool heat pumps move heat from air into water instead of burning fuel, so their output depends on air temperature and humidity. Makers often publish capacity at mild test conditions such as 80°F air; at 50°F the same unit may deliver noticeably less. The calculator multiplies area by the temperature gap and an exposure factor (10 sheltered, 12 average, 15 windy) and applies a cover credit. The result is the output to look for at your cool-month air temperature. Because heat pumps add heat slowly, plan to keep the pool at temperature rather than reheating it from cold each weekend; the heating time calculator shows why. Compare with fuel-burning units in heat pump vs gas pool heater.
Worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 512 sq ft, target 82°F, 60°F average air, average exposure, no cover. Need ≈ 512 × 22 × 12 ≈ 135,000 BTU/h output at 60°F air, about 11.3 tons of output. With a nightly cover the estimate falls to about 95,000 BTU/h.
FAQ
Does a pool heat pump need its own circuit?
Most run on a dedicated 240 V circuit installed by a licensed electrician, sized from the nameplate.
Will it work in spring and fall?
Many lose efficiency below about 50°F air; check the maker's low-temperature limit.
Can two smaller units replace one big one?
Sometimes, with matched plumbing; ask a licensed pool professional.
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