Pool Heater Running-Cost Estimator
Enter your pool volume, current and target water temperature, and your heater's specs, to estimate the run time and cost to heat up — for gas, heat-pump, and resistance heaters.
Heat-up estimate
How the estimate works
Water takes 1 BTU of heat to raise 1 pound by 1°F, and a gallon of water weighs about 8.34 lb, so the total heat needed is pool gallons × 8.34 × the temperature rise in °F. Dividing that by how fast your heater actually delivers usable heat — its input rate multiplied by its efficiency (or, for a heat pump, its COP) — gives the hours it will take. Multiplying the input rate by that run time gives the fuel or electricity consumed, and its cost at your local price.
This is a heat-up estimate, not a full seasonal running cost: once the pool is at temperature, ongoing heat loss from evaporation and wind means it takes additional (usually smaller) top-up energy to hold that temperature, especially on cool nights or without a cover.
Frequently Asked Questions
Why does a heat pump cost less to run than a gas heater?
A gas heater burns fuel directly to make heat, so it can't exceed 100% efficiency. A heat pump instead moves existing heat from the surrounding air into the water, so for every unit of electricity it consumes it can deliver several units of heat — expressed as its coefficient of performance (COP), often around 4-7 in mild weather. That's why a heat pump's 'efficiency' in this calculator can be entered as 400-700%, while a gas heater tops out well under 100%.
Why does a heat pump take longer to heat a pool than a gas heater?
Heat pumps typically have a lower total heat output (BTU/hr) than a similarly priced gas heater, even though they're cheaper to run per BTU delivered. That trade-off — slower to heat, cheaper to maintain temperature — is why heat pumps suit pools kept at a steady temperature all season, while gas heaters suit pools that need to heat up quickly for occasional use.
Does this estimate include ongoing heat loss?
No — this is a one-time heat-up estimate: the energy needed to raise the water from a starting temperature to a target temperature. Keeping a pool at that temperature afterward costs more, since heat is constantly lost to evaporation, wind, and cooler night air — a pool cover is one of the most effective ways to cut that ongoing loss.
Where do I find my heater's input rate and efficiency?
Both are usually printed on the heater's data plate or spec sheet: gas heaters list a BTU/hr input rating and an AFUE or thermal-efficiency percentage; electric heat pumps list a power draw in kW/amps and a COP rating (sometimes given at a specific air temperature). If you can't find the COP, the manufacturer's product page or manual usually lists it.
Planning estimate only, for a one-time heat-up. Actual cost varies with weather, wind, evaporation, whether a cover is used, and your heater's real-world performance — check your utility's current rates and your heater's rated specs for the most accurate figure.