Pool Heater Cost Calculator
Estimate the energy cost to heat your pool from its current temperature to a desired target. Useful when budgeting for gas, electric, or heat-pump heaters.
Last updated: September 2026
Formula below · 1 source (Wikipedia) · Updated Sep 2026
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About this calculator
Heating a pool requires raising the thermal energy of a large water mass. Water has a specific heat of 1 BTU per pound per °F, and one gallon of water weighs approximately 8.34 lb. The energy required in BTUs is: BTUs = poolVolume × 8.34 × (targetTemp − currentTemp). Each heater option carries the useful heat delivered per unit of energy you buy: a gas heater at 85% efficiency delivers 85,000 BTU per therm (100,000 BTU × 0.85), a propane heater at 80% delivers 80,000 BTU per therm, electric resistance delivers 3,412 BTU per kWh, and a heat pump with a COP of 5 delivers about 17,060 BTU per kWh. The formula is: cost = poolVolume × 8.34 × (targetTemp − currentTemp) / heatPerUnit × energyCost, so enter your price per therm for gas or propane and per kWh for electric heaters. Real heat pump COP falls in cool air, and the result ignores heat lost to the air during a long heat-up, so treat it as the minimum cost.
How to use
You have a 20,000-gallon pool at 62 °F and want to reach 80 °F. Your gas heater is 85 % efficient and gas costs $1.20/therm. Temperature rise = 80 − 62 = 18 °F. Heat needed = 20,000 × 8.34 × 18 = 3,002,400 BTU. Therms bought = 3,002,400 / 85,000 ≈ 35.3. Cost = 35.3 × $1.20 ≈ $42.39 to bring the pool up to temperature initially. With a heat pump (COP 5) at $0.15/kWh: 3,002,400 / 17,060 ≈ 176 kWh × $0.15 ≈ $26.40.
Frequently asked questions
How much does it cost to heat a pool by 10 degrees Fahrenheit?
For a 15,000-gallon pool, raising temperature by 10 °F requires approximately 15,000 × 8.34 × 10 = 1,251,000 BTUs of heat energy. With an 85 % efficient gas heater at $1.20/therm, that is (1,251,000 / 0.85) / 100,000 × $1.20 ≈ $17.66. An electric resistance heater at 100 % efficiency at $0.13/kWh converts to about $0.13 per 3,412 BTU, costing roughly $47.70 for the same rise. A heat pump with a COP of 4.0 (400 % efficiency) would cut the electric cost to around $12. The heater type is the single biggest factor in running costs.
What type of pool heater is the cheapest to run?
Heat pumps are the cheapest to operate in most climates because they move heat from the surrounding air rather than generating it, achieving a COP of 3–6 (300–600 % effective efficiency). In warm, sunny climates, solar heating systems have near-zero operating costs after installation. Gas heaters are fast and cost-effective for occasional use or in cold climates where air-source heat pumps lose efficiency. Electric resistance heaters are the most expensive to operate and are generally not recommended for large pools. The best choice depends on your climate, usage frequency, and upfront budget.
How can I reduce my pool heating costs?
Using a pool cover is the single most effective measure — it can reduce heat loss by up to 70 % by preventing evaporative cooling overnight and in wind. Lowering your target temperature by even 2 °F noticeably reduces energy use due to increased heat loss at higher differentials. Running your heater during off-peak electricity hours (if on a time-of-use tariff) also helps. Proper pool insulation, windbreaks around the pool, and a well-maintained heater operating at peak efficiency all contribute to meaningful savings over a season.