Heat Pump vs Gas Heater Calculator
Compare a pool heat pump against a gas heater on the same delivered heat. Get the annual running-cost gap, the upfront difference, and how many seasons it takes to pay back.
Safety
Estimates only. Both figures assume the same delivered heat, which is the fair comparison but not the same experience: a gas heater reaches temperature in hours, a heat pump in a day or more. A heat pump also fades as the air cools — output drops below about 50°F ambient and is negligible near 40°F, so in a cold climate the honest answer is often gas, or a heat pump for the season and gas for the shoulders. Gas work must be done by a licensed installer and vented clear of the pool; a heat pump needs a dedicated 240V circuit to NEC Article 680.
A heat pump delivers 100,000 BTU into the water for about $0.76 against $1.83 for gas at $0.13/kWh and $1.50/therm — roughly 58% cheaper to run. It also costs more to install, typically $5,000 against $3,000. If you were buying a heater anyway, only that $2,000 gap has to be paid back, which takes about one to two seasons; ripping out a gas heater that still works puts the whole $5,000 on the bill and stretches it to three or more. Enter your own quotes and fuel prices above.
Heat Pump vs Gas Payback Chart
This decision is settled by two prices, and neither of them is on the heater: what you pay for a therm of gas and what you pay for a kilowatt-hour. The chart crosses the two at the same delivered heat — annual saving on top, payback in seasons underneath.
| Gas price | Gas bill | $0.10/kWh | $0.13/kWh | $0.20/kWh | $0.30/kWh |
|---|---|---|---|---|---|
| $1.00/therm cheap gas | $1,756/yr | $912/yr 2.2 seasons | $659/yr 3.0 seasons | $68/yr 29.4 seasons | gas wins no payback |
| $1.50/therm US average | $2,634/yr | $1,790/yr 1.1 seasons | $1,537/yr 1.3 seasons | $946/yr 2.1 seasons | $102/yr 19.6 seasons |
| $2.00/therm dear gas | $3,512/yr | $2,668/yr 0.7 seasons | $2,415/yr 0.8 seasons | $1,824/yr 1.1 seasons | $980/yr 2.0 seasons |
| $3.28/therm propane at $3/gal | $5,760/yr | $4,916/yr 0.4 seasons | $4,663/yr 0.4 seasons | $4,072/yr 0.5 seasons | $3,228/yr 0.6 seasons |
Assumes both heaters deliver 200,000 BTU/hr for 4 hours a day over a 6-month season, gas at 82% efficiency, a heat pump at COP 5.0, and a $2,000 difference between the two installed quotes. Replacing a gas heater that still works means paying back the whole heat pump instead, so multiply the seasons by roughly two and a half.
Why the running costs are so far apart
A gas heater makes heat and a heat pump moves it, and that is the whole story. Burning a therm gets you about 82,000 BTU into the water, because roughly 18% goes up the flue. A heat pump takes 1 kWh — 3,412 BTU of electricity — and uses it to shift four or five times that much heat out of the outside air, which is what a coefficient of performance of 5.0 means. Nothing is being created out of nothing; the heat was already in your backyard and the compressor is only paying for the transport.
Put both on the same 100,000 BTU delivered and the arithmetic is short. Gas: 1.22 therms at $1.50 is $1.83. Heat pump: 5.9 kWh at $0.13 is $0.76. Same warm water, less than half the money — and the ratio, not either price on its own, is what the chart above is really showing. Cheap gas next to expensive electricity can close the gap completely, which is why the calculator lets both move.
The 50°F wall
A heat pump can only move heat that is out there to be moved. Down to about 50°F of ambient air it performs close to its rating. Below that, capacity falls away quickly, and somewhere near 40°F it will run all day without moving the thermometer. Manufacturers rate their units at warm-air conditions, so the COP printed on the box is the best case, not the April case — drop the COP slider above to 3.5 if you are sizing for shoulder-season use.
That single limitation is why gas heaters still sell. A gas heater does not care what the weather is doing, and it raises water temperature in hours rather than in a day or two, which is the difference between heating a pool for Saturday and heating a pool for the season. In a cold climate the honest comparison is often not one or the other but both: the heat pump carries the season, the gas heater covers the cold snaps and the spa.
Buying either way, or replacing something that works
These are two different questions and they get very different answers, which is why the switch above changes the result so much. If your pool has no heater, or the old one has failed, you are spending money on a heater regardless — so the cost of choosing the heat pump is only the difference between the two quotes, commonly $1,500–$2,500. At a typical season's saving that is paid back in a season or two.
Tearing out a gas heater that still runs is a different trade: the whole installed price of the heat pump is the price of the decision, and the payback roughly doubles. Unless gas is expensive where you live, the cheaper move is usually to plan the switch, budget for it, and make it the day the old heater fails. Do check what the electrical work costs before committing either way — a heat pump needs a dedicated 240V circuit, and if the panel is full or the run is long that line item can be larger than the difference between the two heaters.
Before you buy either one
Size the heater first — an undersized unit of either type runs constantly and never quite arrives, and both are sized from surface area rather than gallons in the pool heater size calculator. Then buy a cover. A cover cuts heat loss by 50–70%, which beats the efficiency difference between the two heaters and shortens the payback on whichever one you pick, because it cuts the hours both of them have to run.
For the month-by-month running figure on the heater you already own, use the pool heating cost calculator; the cost to run a pool heat pump guide works through the COP maths in full, and pool heater types compared brings solar into the picture, which has the lowest running cost of anything here if you have the roof space for it.