Pool Heating Cost Calculator
Estimate the energy and fuel cost to heat your pool a set number of degrees, for gas, propane or electric heaters.
How it works
BTU to heat = gallons × 8.34 × °F rise · input BTU = heat ÷ efficiency · cost = input ÷ (fuel energy content) × fuel price
Raising water temperature takes a fixed amount of energy: one BTU lifts one pound of water one degree Fahrenheit, and a gallon weighs 8.34 pounds. Divide that heat by the heater’s efficiency to get the fuel energy you must buy, then convert to therms of gas (100,000 BTU each), gallons of propane (91,500 BTU each) or kWh of electricity (3,412 BTU each) at your price. A heat pump’s "efficiency" above 100% is its COP — it moves several units of heat per unit of electricity.
Worked example
Heating 15,000 gallons by 10°F needs 15,000 × 8.34 × 10 = 1,251,000 BTU. A gas heater at 82% must burn 1,251,000 ÷ 0.82 ≈ 1,525,600 BTU = 15.3 therms; at $1.50/therm that’s about $22.90 for the heat-up, or $2.29 per degree.
Frequently asked questions
Why does keeping a pool warm cost so much more than one heat-up?
A pool loses heat continuously — mostly to evaporation — so the heater keeps replacing it. An uncovered pool can lose several degrees overnight, meaning you pay to reheat it again and again. A solar or bubble cover cuts that loss by 50–70%.
Is an electric heat pump cheaper than gas?
Usually yes to run, because a heat pump’s COP of 4–6 means it delivers 4–6 BTU of heat per BTU of electricity bought. It heats more slowly and works poorly in cold air, so gas wins for fast heat-ups and early/late season.
How long will heating take?
Divide the BTU needed by the heater’s output rating. A 400,000 BTU/hr gas heater on the 1.25M-BTU example above takes roughly 1,525,600 ÷ 400,000 ≈ 3.8 hours to raise the pool 10°F, ignoring simultaneous heat loss.
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This calculator is for educational purposes. Double-check important results before acting on them.