What it costs to heat a pool
The heat a pool needs depends only on how much water it holds and how many degrees you raise it (see the pool heater size calculator). What changes between heaters is how much you pay for each unit of that heat. A gas heater burns fuel and loses some of it up the flue; an electric element turns each kWh into one kWh of heat; a heat pump moves heat from the outside air into the water and delivers several kWh of heat for each kWh of electricity it uses.
Heat (kWh) = litres × °C rise × 0.001163 (or US gallons × 8.34 × °F rise ÷ 3,412)
Heat pump cost = heat ÷ COP × electricity price
Electric heater cost = heat × electricity price
Gas cost = heat ÷ efficiency × gas price (1 therm = 100,000 BTU = 29.3 kWh; 1 kWh = 3.6 MJ)
Propane: 1 US gallon ≈ 91,452 BTU
Worked example: 15,000 gallons raised 17 °F
The pool needs about 2.13 million BTU (624 kWh) of heat.
| Heater | Energy bought | Cost |
|---|---|---|
| Heat pump, COP 5, $0.17/kWh | 124.7 kWh | $21.21 |
| Natural gas, 84%, $1.50/therm | 25.3 therms | $38.00 |
| Propane, 84%, $2.80/gal | 27.7 gallons | $77.57 |
| Electric resistance, $0.17/kWh | 624 kWh | $106.03 |
In Australia, a 50,000-litre pool raised 10 °C needs 581.5 kWh of heat: about A$34.89 with a COP 5 heat pump at A$0.30/kWh, or about A$99.69 with an 84% gas heater at A$0.04 per MJ. In the UK, the same heat from an 84% gas heater at £0.07 per kWh of gas costs about £48.46.
Heat-up versus keeping warm
This calculator prices the heat to raise the temperature. Keeping a pool warm afterwards means replacing the heat it loses every day, mostly through evaporation, which depends on weather, wind, shade and whether you use a cover. Enter the number of heat-ups per month that matches how you use the pool (for example 4 if you let it cool during the week and reheat each weekend) to compare options. A good cover cuts the keep-warm cost more than anything else; the US Department of Energy notes that covering a pool when it is not in use is the single most effective way to reduce pool heating costs.
About heat pump COP
The coefficient of performance (COP) is heat delivered divided by electricity used. Pool heat pumps commonly list COPs of around 4 to 6 at mild test conditions, but the COP falls as the air gets colder, so a heat pump that is very cheap to run in summer costs more in spring and autumn and may struggle below about 10 °C (50 °F). Use the COP from the manufacturer's table at the air temperature you expect.
Finding your energy prices
- Electricity: the unit rate per kWh on your bill (leave out fixed daily charges).
- Natural gas: US bills show therms (sometimes CCF, roughly one therm); UK and European bills show kWh; Australian bills show MJ.
- Propane: your delivered price per gallon (or per litre: 1 US gallon = 3.785 L).
Common mistakes
- Comparing heater ratings instead of running cost. A bigger heater heats faster but does not need less energy.
- Using the best-case COP all year.
- Forgetting the pump. The filter pump runs while heating; see the pool pump cost calculator.
Estimates exclude heat loss during heating. Actual costs depend on weather, cover use and your tariff.
Cost by temperature rise (15,000 gallons)
Cost of one heat-up at the example prices: electricity $0.17/kWh (heat pump COP 5), natural gas $1.50/therm and propane $2.80/gal (84% efficient heaters).
| Rise | Heat needed | Heat pump | Natural gas | Propane | Electric element |
|---|---|---|---|---|---|
| 5 °F | 183 kWh | $6.24 | $11.18 | $22.81 | $31.18 |
| 10 °F | 367 kWh | $12.47 | $22.35 | $45.63 | $62.37 |
| 15 °F | 550 kWh | $18.71 | $33.53 | $68.44 | $93.55 |
| 20 °F | 734 kWh | $24.95 | $44.71 | $91.25 | $124.74 |
The ranking can change with your local prices: where electricity is expensive and gas is cheap, or in cold weather when a heat pump's COP falls, gas can come out ahead. Enter your own prices above to see which is cheapest for you.
Frequently asked questions
Is a heat pump cheaper than gas for heating a pool?
Usually per unit of heat. Heating 15,000 gallons by 17 °F costs about $21 with a COP 5 heat pump at $0.17/kWh versus about $38 with natural gas at $1.50/therm and 84% efficiency, but a heat pump heats more slowly.
How much does it cost to heat a pool with propane?
Raising 15,000 gallons by 17 °F with an 84% efficient heater uses about 27.7 gallons of propane: about $78 at $2.80 per gallon.
How much does it cost to heat a 50,000 litre pool?
Raising it 10 °C needs about 581 kWh of heat: about A$35 with a COP 5 heat pump at A$0.30/kWh.
How many kWh is a therm?
One therm is 100,000 BTU, about 29.3 kWh.
How much does it cost to raise a pool 10 degrees?
For 15,000 gallons, about 367 kWh of heat: roughly $12 with a COP 5 heat pump at $0.17/kWh, $22 with natural gas at $1.50/therm, or $46 with propane at $2.80/gal (84% efficiency).
Sources
- US Energy Information Administration: Units and calculators (therm, propane ≈ 91,452 BTU per gallon, kWh = 3,412 BTU).
- US Department of Energy, Energy Saver: heat pump and gas pool heaters, swimming pool covers.
Last reviewed 28 October 2026. Results are estimates; see our disclaimer.