Home › Heater size
Pool heater size calculator
It takes 1 BTU to warm one pound of water by 1°F, and a gallon of water weighs 8.34 lb. That gives the heat needed; your heating time and heater efficiency give the size.
BTU/hr for a 20°F rise in 24 hours, at 82% efficiency
| Pool size | BTU/hr |
|---|---|
| 5,000 gal | 42,378 |
| 10,000 gal | 84,756 |
| 15,000 gal | 127,134 |
| 20,000 gal | 169,512 |
| 30,000 gal | 254,268 |
What the number leaves out
The result is for the water alone. An uncovered pool loses heat through evaporation, so a cover is often the cheapest upgrade you can make. Heat pumps are rated differently, and they lose output in cold air, so check their rating at your air temperature.