Pool Heating Cost Calculator
Enter pool volume, the temperature rise you want, heater efficiency and your energy price.
Result
How it is calculated
Volume is in US gallons, the temperature rise in °F, the heater efficiency in percent (1 to 100) and the price per kWh of the energy the heater uses. Water weighs 8.34 lb per gallon and needs 1 BTU per pound per °F, so heat needed (BTU) = gallons × 8.34 × rise. With 1 kWh = 3,412.142 BTU, net kWh = BTU / 3,412.142, and the energy used is kWh in = net kWh / efficiency. Then cost = kWh in × price and cost per degree = cost / rise. Efficiency cannot exceed 100 %, so a heat pump with a COP of 4 cannot be entered directly: you can instead divide your electricity price by the COP and enter 100. Heat lost to air, wind and evaporation, and the cost of keeping the pool warm, are not included. To convert, 1 m³ = 264.17 US gallons and a rise of 1 °C = 1.8 °F.
Worked example
A 15,000-gallon pool, a 10 °F rise, an 85 % efficient heater and energy at 0.15 per kWh. Heat needed = 15,000 × 8.34 × 10 = 1,251,000 BTU, which is 1.25 MMBtu or 366.6 kWh of net heat. Energy used = 366.6 / 0.85 = 431.33 kWh. Cost = 431.33 × 0.15 = $64.70. That is $6.47 per °F. Heating by 20 °F would double both the energy and the cost.
Common mistakes
- Entering the volume in litres or cubic metres: the field is in US gallons, so a 60 m³ pool must be entered as about 15,850.
- Entering the temperature rise in °C: the field is °F, and a 10 °C rise is 18 °F.
- Entering a heat pump's COP (such as 4) as efficiency: the field accepts up to 100 and returns nothing above it.
- Assuming the result is the cost of a season: it is the cost of the initial rise only, and it excludes the heat the pool loses every day to air and evaporation.
- Using the gas price per therm or per cubic metre while the field wants a price per kWh.
About this calculator
Heating a pool by a given temperature rise takes a fixed amount of energy determined by physics — energy = pool volume × water's specific heat × temperature rise — and the calculator then divides that by your heater's efficiency (a percentage of up to 100), since gas heaters typically run at 80–95% efficiency and electric resistance heaters near 100%. Heat pumps deliver a coefficient of performance of roughly 4–6 (meaning they move 4–6 units of heat per unit of electricity consumed), which is above 100% and so cannot be entered as an efficiency; to estimate a heat pump, set the efficiency to 100% and divide the energy and cost by its COP. The energy result in kWh is then multiplied by your local energy price to get the cost.
Pool owners run this calculation when comparing heater types before purchase, since a heat pump's much higher COP can make it dramatically cheaper to run than a gas heater or electric resistance heater despite a higher upfront cost, or when deciding whether it's worth heating the pool at all for a short swim season.
This calculator takes your pool volume in US gallons, desired temperature rise in °F, heater efficiency and energy price per kWh, and returns the energy needed and what it will cost.
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