calculators

Pool Heater Running Cost Calculator — By Fuel Type

Estimate what a pool heater costs to run per hour, day and season at your own fuel rates — natural gas, propane, electricity or heat pump — with cost per million BTU compared.

Last updated: 2026-10-31

Quick answer

Running cost is fuel math, not opinion: cost/hr = rated input ÷ energy per fuel unit × your price. A "400,000 BTU" natural gas heater burns 4 therms an hour — at $1.80/therm, about $7.20 per running hour. The same heat delivered from a heat pump (COP 5) costs roughly $1.90/hour at $0.17/kWh, which is why heat pumps dominate in warm climates and gas wins where winters are cold. The calculator prices your exact model at your rates, for the hour, the day and the season.

Industry / community reference · 2026-10-31

The billing units, decoded

Natural gas is billed in therms: 1 therm = 100,000 BTU of fuel, and your heater turns ≥82% of that into water heat (the federal floor, 10 CFR 430.32). A 400k BTU/hr input heater runs 4 therms/hour.
Propane is billed in gallons: one gallon holds ≈ 91,502 BTU. Propane heaters burn the same way as gas but the fuel price per BTU is usually higher — check the per-million-BTU bar in the result.
Electricity is billed in kWh: 1 kWh = 3,412 BTU. A resistance heater turns all of it into heat (no flue loss) but pays full price for every BTU; a heat pump multiplies each kWh roughly 5× at warm-air COP 5.

Official regulation text (eCFR) · 2026-10-31

Edit the prices to your bill

The default prices are typical U.S. residential averages — they're a starting point, not a quote. Your utility bill states the real $/therm or $/kWh; propane is quoted per gallon by your supplier. Ten seconds of editing makes every figure in the result yours, and the per-million-BTU comparison re-bars instantly so you can sanity-check quotes like "a heat pump pays for itself in two seasons."

What moves the seasonal bill

Hours per day — maintaining temperature costs far less than recovering it; a solar cover stretches the time the heat stays in (DOE: covers cut evaporation 30–50%).
Season length — the calculator's 90/120/180-day presets frame the difference between Memorial-to-Labor-Day and year-round swimming.
The ×12 loss you're fighting — maintaining a pool costs area × rise × 12 BTU/hr continuously; the sizing guide shows where that number comes from.

Agency guidance (DOE / EPA) · 2026-10-31

Reading the result honestly

The seasonal figure assumes the heater runs to hold temperature, not that it recovers from a cold soak every morning — a covered pool sags a degree or two overnight, an uncovered one can lose several. That is why the same heater can produce two very different seasonal bills at identical rates, and why cover discipline is the cheapest line item in pool heating. Treat the per-million-BTU comparison as the stable part of the answer: fuel prices move, but the conversion efficiency of each heater type is set by physics and the federal floor.

Inferred

From here

Cost per season is only half the decision — the other half is equipment price and climate behavior. Run the same pool through the heat pump vs gas calculator, or size the heater first in the BTU calculator if you haven't yet.

FAQ

How much does it cost to run a pool heater per hour?

A 400,000 BTU/hr input natural gas heater burns 4 therms per hour; at $1.80/therm that's about $7.20/hour of continuous running (about $5.90/hour of that becomes heat at 82% efficiency). A comparable heat pump at COP 5 costs roughly $1.90/hour at $0.17/kWh. Enter your own rates in the calculator above for exact figures.

Is a pool heat pump cheaper to run than gas?

Per BTU of heat, usually yes — at typical U.S. rates a heat pump delivers each million BTU for roughly a third of natural gas's price and far less than propane. The catch is air temperature: heat pump output and COP fall in cold weather, exactly when you want heating, and heat pumps cost more upfront.

Why does the calculator bill gas heaters on input?

Utility meters measure fuel burned, and gas heaters are rated by fuel input — only ≥82% of it becomes water heat under the federal minimum (10 CFR 430.32). Billing anything else would understate the real cost.