Pool Heating Cost Calculator
Estimate the energy and cost to raise your pool's temperature by a chosen number of degrees.
Raising water temperature takes 8.34 BTU per gallon per degree Fahrenheit. A gas therm holds 100,000 BTU and a kilowatt-hour about 3,412 BTU. Gas heaters lose some heat up the flue (efficiency), while a heat pump multiplies each unit of electricity by its COP. This is the heat-up energy only — an uncovered pool keeps losing heat to the air, so real running costs run higher. A cover cuts that loss a lot.
How it works
Heating water is pure physics: it takes 8.34 BTU to raise one gallon by one degree Fahrenheit. Multiply by your gallons and the degrees you want to gain and you get the total heat needed.
From there we convert to fuel. A gas therm holds 100,000 BTU, but a heater only delivers a fraction of that to the water — its efficiency, often around 80 to 84%. A heat pump runs on electricity and multiplies each kilowatt-hour by its COP, so a COP of 5 means five units of heat for every unit of power.
This figures the one-time heat-up energy, not the ongoing losses. An uncovered pool bleeds heat to the air constantly through evaporation, so the real cost to hold a temperature runs higher — a solar or bubble cover is the single biggest money-saver.
Frequently asked questions
Why is my real bill higher than this estimate?
This is the energy to heat the water once. Pools lose heat continuously, mostly through evaporation, so keeping the water warm day after day costs more than a single heat-up. A cover cuts that loss dramatically.
Gas heater or heat pump — which is cheaper to run?
Heat pumps are usually far cheaper per degree because they move heat rather than burn fuel, but they're slow and struggle in cold air. Gas heats fast in any weather but costs more per therm of output. Your local energy prices decide the winner.
What COP should I enter for a heat pump?
Most modern pool heat pumps land between 4 and 6 under mild conditions, meaning four to six units of heat per unit of electricity. Efficiency drops in colder air, so use a lower number for early-spring or late-fall heating.