Pool Heating Cost Calculator
Estimate what it costs to heat your pool with gas or a heat pump, using your own energy rate — no tariff is stored, so the answer never goes stale.
Calculator
Heating 15,000 gallons by 10 °F with gas uses 15.26 therms ≈ $22.88 at $1.50/therm.
Heating cost comes down to one number — the energy your pool needs — priced at your own utility rate. This calculator works out the energy from your volume and temperature rise, then converts it to a fuel bill two ways: therms for a gas heater and kilowatt-hours for a heat pump. You enter the rate, so the result reflects your bill and stays correct no matter how gas and electricity prices move. Nothing here is hardcoded to a tariff or a date.
Pick the energy source, type in your rate (dollars per therm for gas, dollars per kWh for a heat pump), and adjust the efficiency or COP if you know your equipment's figures. The default 82% gas efficiency and a COP of 5 are reasonable starting points for a typical setup.
Formula
First the energy, then the fuel it takes to supply it at your rate:
BTU = gallons × 8.34 × ΔT
Gas: therms = BTU ÷ 100,000 ÷ efficiency, then cost = therms × rate.
Heat pump: kWh = BTU ÷ 3,412 ÷ COP, then cost = kWh × rate.
- 100,000 — BTU in one therm of natural gas.
- 3,412 — BTU in one kilowatt-hour.
- efficiency — how much fuel energy reaches the water (~0.82 for gas).
- COP — heat delivered per unit of electricity (~5 for a heat pump).
Worked example
Warming a 15,000-gallon pool by 10 °F needs 15,000 × 8.34 × 10 = 1,251,000 BTU.
Gas at 82% and $1.50/therm: 1,251,000 ÷ 100,000 ÷ 0.82 = 15.26 therms × $1.50 = $22.89.
Heat pump at COP 5 and $0.15/kWh: 1,251,000 ÷ 3,412 ÷ 5 = 73.3 kWh × $0.15 = $11.00.
Same heat-up, roughly half the cost on the heat pump — the gap that makes heat pumps popular in mild climates.
Reading the running cost
This is the cost of a single heat-up — raising the pool by the degrees you entered, one time. Real running cost over a season is higher, because a heated pool constantly loses heat to the air and to evaporation and the heater keeps topping it back up. The per-heat-up figure is still the right way to compare options, though: it isolates the physics from the weather and lets you put gas and a heat pump side by side on equal terms.
Two things dominate the bill. The first is the temperature rise — energy is directly proportional to ΔT, so heating to 88 °F instead of 82 °F is not a small premium, it is a proportional one, and it recurs every time the pool cools. The second is heat loss, most of it evaporative and most of it preventable with a cover; a solar or bubble cover routinely cuts heating cost by a large fraction because the heater spends far less time replacing lost heat. Beyond that, the source you choose sets the baseline: gas gives speed at a higher per-BTU price, while a heat pump trades speed for a much lower running cost wherever the outside air stays mild. Because you supply the rate, you can re-run this any time your utility price changes and get a current answer — the tool never needs updating to stay accurate.
The dollar figure is an estimate from standard energy constants and the rate you enter. Check your own utility bill for the exact price per therm or kWh, and remember that gas efficiency and heat-pump COP vary by model and, for the heat pump, by outside air temperature.
Frequently asked questions
How much does it cost to heat a pool?
It depends on your pool size, the temperature rise and your energy rate. Warming a 15,000-gallon pool 10 °F costs about $22.89 on gas at $1.50/therm, or about $11.00 on a heat pump at $0.15/kWh. Enter your own rate above.
Is a heat pump really cheaper than gas?
In mild climates, usually by a wide margin. A COP of 5 means the heat pump delivers about five units of heat per unit of electricity, so the same heat-up can cost roughly half of gas — compare the two with your own rates above.
Why do you ask me for the energy rate?
Because energy prices change and vary by region. Storing a tariff would make the tool wrong the moment prices moved. You enter your own $/therm or $/kWh, so the answer is always current and specific to you.
What is a therm and how many BTUs is it?
A therm is the standard billing unit for natural gas and equals 100,000 BTU. Gas heaters are less than 100% efficient, so the tool divides by efficiency to find the therms you actually pay for.
Does this include heat lost overnight?
No — it is the cost of one heat-up. A pool loses heat continuously, so season-long cost is higher. A cover is the cheapest way to cut that ongoing loss and the biggest single saving on your bill.
What efficiency and COP should I use?
About 0.82 for a typical gas heater and a COP near 5 for a heat pump are reasonable defaults. If your equipment lists its own figures, enter those — heat-pump COP in particular falls as the outside air gets colder.