Pool heat pump size calculator
A heat pump has to replace the heat your pool loses to the air. Here is how big it needs to be.
In short: Heat pump size in BTU per hour ≈ pool surface in ft² × (pool temperature − air temperature) × 12. A 16 × 32 ft pool kept at 82 °F in 70 °F air needs about 74,000 BTU/h: an 85k heat pump.
Formulas reviewed November 1, 2026 · How we calculate
Using your saved pool: . My pool
85k BTU heat pump
To hold 82 °F when the air averages 70 °F, your pool needs about 74k BTU an hour.
- Heat needed
- 73,728 BTU/h
- Pool above air
- 12 °F
- Water surface
- 512 ft²
What to add
What would change your result
- Swimming at 80 °F instead of 82 °F cuts the heat needed by 17%.
- A cover at night keeps most of the day's heat. Without one, consider the next size up.
- Heating a cold pool quickly for a weekend? A gas heater fits that better.Open
A rule of thumb for light wind. Exposed pools, high altitude and pools without a cover lose heat faster.
Next, for this pool
Pool heat pump size chart
Heat pump size by water surface and how much warmer than the air you keep the pool.
| Water surface | 10 °F above air | 15 °F above air | 20 °F above air |
|---|---|---|---|
| 300 ft² | 50k BTU | 65k BTU | 85k BTU |
| 400 ft² | 50k BTU | 85k BTU | 100k BTU |
| 512 ft² | 65k BTU | 100k BTU | 125k BTU |
| 600 ft² | 85k BTU | 110k BTU | Over 140k BTU |
| 800 ft² | 100k BTU | Over 140k BTU | Over 140k BTU |
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Size for your coldest swimming month. Use the average air temperature of the coolest month you want to swim in, not the summer average.
Wind and no cover need more. The 12 BTU rule assumes light wind. Exposed pools, or pools that are never covered, often need the next size up.
Heat pumps are slow but cheap to run. They hold a temperature well but take days to warm a cold pool from scratch. Start them early in the season.
Below about 50 °F most heat pumps lose much of their output. In cold climates, a gas heater or a hybrid makes more sense.
Key facts
- Most of a pool's heat leaves through the surface, which is why surface area, not volume, sets heat pump size.
- Residential pool heat pumps commonly range from about 50,000 to 140,000 BTU an hour.
- Heat pump output drops as the air gets colder; check the rating at the temperatures you swim in.
How it's calculated
Heat needed = water surface (ft²) × (pool temperature − air temperature) × 12 BTU per hour.
The 12 is a common sizing factor for heat lost through the surface in light wind. The result is rounded up to a standard heat pump size.
Questions people ask
What size heat pump do I need for my pool?
Surface area × (pool temperature − air temperature) × 12. For a 16 × 32 ft pool at 82 °F with 70 °F air, about 74,000 BTU/h, so an 85k unit.
Can a heat pump be too big?
A larger unit heats faster and works less hard, but costs more upfront. Too small is the common mistake: it never catches up on cool nights.
How long does a heat pump take to heat a pool?
Often two to four days from cold, depending on size and weather. Heat pumps are best at holding a temperature.
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