Pool heating cost calculator
The heater’s price is paid once; the fuel is paid every month you swim. This prices the same heat three ways — gas, heat pump and plain electric resistance — so you can see which one your utility rates actually favour.
Pre-filled with a 16 × 32 ft pool. Change any field — the prices start at the EIA averages and are yours to overwrite with the numbers on your own bills.
Cheapest to hold temperature: Heat pump
$146per month
- Gas heater$437/mo
- Heat pump$146/mo
- Electric resistance$729/mo
| Heater | One heat-up | Per month | Season |
|---|---|---|---|
| Gas heater | $73 | $437171 therm | $2,256 |
| Heat pump | $24 | $146843 kWh | $754 |
| Electric resistance | $122 | $7294,215 kWh | $3,768 |
- Water in the pool
- 19,150 gal = 159,808 lb
- Heat-up, lb × °F
- 2.4 million BTU
- Month, lb × °F/day × days
- 14.38 million BTU
- Season, heat-up + months
- 74.31 million BTU
Defaults: US EIA, July 2026 residential price ($26.45 per thousand cubic feet ≈ $2.55/therm) and US EIA, 2025 average residential price, read 2026-10-18. Gas ÷ efficiency ÷ 100,000 BTU per therm; electricity ÷ COP ÷ 3,412 BTU per kWh. Pump power is not included.
Sizing the heater instead?
Output in BTU per hour is a different question — the heater size calculator answers it.
What it measures
Two quantities of heat. The first is the heat-up: every pound of water in the pool times every degree you want to add. The second is the upkeep: the degrees the pool loses each day to evaporation, the night sky and the ground, which the heater has to put back to hold the temperature. Over a season the upkeep is almost always the larger bill, which is why the tool asks for it separately.
Each quantity is then bought three ways. A gas heater burns fuel and loses part of it up the flue, so the heat is divided by its efficiency. A heat pump moves heat out of the air, so the heat is divided by its coefficient of performance (COP). An electric resistance heater turns one kilowatt-hour into one kilowatt-hour of heat, no more — the baseline the US Department of Energy measures heat pumps against.
How to use it
- Enter surface area and average depth. If you only know gallons, the pool volume calculator works back from the shape.
- Set the heat-up: the gap between the water when you open and the temperature you swim at.
- Measure the daily loss rather than guessing it: heater off, read a thermometer at dusk, read it again at dusk the next day. Do it with the cover on if you use one.
- Replace the two prices with the ones on your gas and electric bills, and the efficiency and COP with the figures on your heater’s spec sheet.
Worked example
The tool’s opening numbers: a 512 ft² pool, 5 ft deep on average, heated 15 °F once and then topped up 3 °F a day for 30 days a month over 5 months, at $2.55 a therm and 17.3¢ a kWh.
| Step | Working | Result |
|---|---|---|
| Gallons | 512 × 5 × 7.48 | 19,150 gal |
| Pounds of water | gallons × 8.345 | 159,808 lb |
| Heat-up | lb × 15 °F | 2.4 M BTU |
| One month of upkeep | lb × 3 °F × 30 | 14.38 M BTU |
| Gas heater, month | ÷ 0.84 ÷ 100,000 = 171 therms | $437 |
| Heat pump, month | ÷ 5.0 ÷ 3,412 = 843 kWh | $146 |
| Electric resistance, month | ÷ 3,412 = 4,215 kWh | $729 |
Same water, same heat, and the monthly bill runs from $146 (heat pump) to $729 (electric resistance). A heat pump’s COP multiplies every kilowatt-hour; a resistance heater multiplies nothing; gas sits on its own price. Change the gas price to a low local tariff, or the COP to what a heat pump manages on a cold night, and watch the order move.
The COP on the box is a warm-weather number
Federal rules rate heat pump pool heaters at one fixed warm, mid-humidity air condition, and the Department of Energy notes many are rated at a COP of 6.0 there. Its own cost analysis adjusts that down for real outdoor air. The tool opens at 5.0 for that reason; in the shoulder months of a cold climate, try lower.
Notes before you trust a number
- Gas efficiency. A gas pool heater made since 2013 must reach at least 82% thermal efficiency, and ENERGY STAR puts the best on the market at 95%. The default sits between.
- The cover. ENERGY STAR says covering the pool when it is not in use can cut heating costs by 50–70%. In this tool that shows up as a smaller daily loss — measure it both ways. The cover comparison covers which kind holds heat.
- Pump power is extra. Every heater needs water moving through it, and a heat pump runs longer hours. Price the pump separately — the variable-speed vs single-speed comparison works that cost out.
- Propane. The gas field is priced per therm of natural gas. Propane is sold by the gallon, so convert your price to a therm basis before you enter it.
For the trade-offs that are not money — speed, climate fit, venting — read the gas vs heat pump vs solar comparison, and when an existing heater stops making heat, the heater repair guide.