What Does It Actually Cost To Run A Pool Heater?
What will it cost to heat your pool?
Fuel and electricity prices vary a lot by region, so put in your own rate from your last bill and get a number that's actually yours.
You need to raise the water 16 degrees
And what about month to month?
Warming the pool up is a one-off. Most of what you'll actually spend is holding that temperature — replacing the heat your pool loses to the air, day and night.
Day and night averaged together, for the month you're picturing.
Per month
$0.00
—
Per month — no cover
$0.00
—
Keeping a solar cover on saves roughly $0.00 a month here — most of a heated pool's heat leaves by evaporation off an open surface, so a cover is the cheapest thing you can do to bring this figure down.
This heater can't hold that temperature in this weather. The pool would be losing heat faster than the unit can replace it, so the water will sit below your target no matter how long it runs. Size up, add a cover, or aim for a lower temperature.
No heating needed. With the air this warm relative to your target, your pool should hold temperature on its own.
Warm-up figures are the physics with no heat loss. Your pool loses heat to evaporation, wind and cool air the whole time the heater runs, so those numbers are a floor, not a forecast. The real-world line adds a typical 25–50%.
Monthly figures are an estimate, and a rough one. They assume you hold your target around the clock for 30 days. Real heat loss swings a long way with wind, humidity and how much sun your pool gets — an exposed, windy yard can run well above these numbers and a sheltered sunny one below. Treat them as a ballpark for comparing options, not a quote.
Check this before you trust the heat pump number. Heat pumps pull warmth out of the air, so they lose capacity as it gets cold — noticeably below about 50°F, and most units shut off entirely somewhere around 40–45°F. In a cold-season climate this heat-up may not be achievable at all.
Above 2,000 feet? High-altitude gas heaters are configured to fire at a reduced rate, so heat-up takes longer than shown — roughly 4% longer per 1,000 feet above 2,000. Your cost stays about the same, because you're buying BTUs rather than hours. Elevation does change which unit you should order — see which Raypak heater you need.
Warm-up uses gallons × 8.34 × degrees of rise. Monthly uses an estimated heat loss across your pool's surface area against the temperature difference with the air, at 82% thermal efficiency for gas. Pool presets assume 4 ft of water in a 52" wall and 3.5 ft in a 48" wall. Estimates only. Not sure of your pool volume or which heater fits? Get in touch.
"How much does it cost to run?" is the question that decides most heater purchases, and almost nobody answers it properly. You'll find articles quoting a monthly figure as if fuel costs the same in Indiana and California, or as if a 12-foot pool and a 24-foot pool are the same problem.
So instead of giving you a number that's wrong for your situation, here's how to calculate yours. It takes about five minutes and one look at a utility bill.
Start here: what heating actually costs, physically
Every heating calculation begins with the same fact.
It takes one BTU to raise one pound of water by one degree Fahrenheit. Water weighs about 8.34 pounds per gallon.
So the energy your pool needs is:
Gallons × 8.34 × Degrees of rise = BTUs required
That's it. Everything else is about how efficiently your equipment delivers those BTUs and what the fuel costs.
Common above ground volumes, for reference:
| Pool | Approximate gallons |
|---|---|
| 15' round, 52" wall | ~5,300 |
| 18' round, 52" wall | ~7,600 |
| 24' round, 52" wall | ~13,500 |
| 18' x 33' oval, 52" wall | ~14,000 |
Worked example. An 18' round pool, raising the water 10°F:
7,600 × 8.34 × 10 = 633,840 BTUs
Gas heaters: converting BTUs to dollars
Gas heaters are rated by BTU input per hour. The Raypak Digital units we carry come in 266,000, 336,000 and 406,000 BTU sizes, and they run at 82% thermal efficiency — meaning 82% of the fuel energy ends up in your water and the rest leaves through the exhaust.
If you're on natural gas
Natural gas is billed in therms. One therm = 100,000 BTUs.
Heater BTU input ÷ 100,000 = therms burned per hour
A 266,000 BTU heater burns about 2.66 therms per hour at full fire.
Now find the rate. Pull out your gas bill and look for the total cost per therm — not just the commodity charge, but the all-in number including delivery. Then:
2.66 × your cost per therm = cost per hour of running
If you're on propane
Propane holds roughly 91,500 BTUs per gallon.
Heater BTU input ÷ 91,500 = gallons burned per hour
A 266,000 BTU heater uses about 2.9 gallons per hour. Multiply by your delivered price per gallon.
Propane is usually the more expensive fuel, and it's worth knowing that before you commit — a heater that's affordable to run on natural gas may not be on propane.
Putting it together
Back to the 18' pool needing 633,840 BTUs for a 10° rise.
A 266,000 BTU heater at 82% efficiency delivers about 218,000 BTUs per hour into the water.
633,840 ÷ 218,000 = about 2.9 hours of run time.
So: 2.9 hours × 2.66 therms/hour × your therm rate = the cost of that 10-degree heat-up. Plug in your own rate and you have a real, specific number for your pool.
Repeat the exercise for a 24' round pool — 13,500 gallons — and you'll see the run time roughly double. Volume is the biggest lever in the whole equation, which is one more reason the size decision matters.
Heat pumps: converting BTUs to kilowatt-hours
Heat pumps are rated two ways: BTU output per hour, and COP — coefficient of performance. A COP of 5 means five units of heat delivered per unit of electricity consumed.
BTU output ÷ COP ÷ 3,412 = kilowatts drawn
(3,412 is simply the number of BTUs in a kilowatt-hour.)
A 100,000 BTU heat pump at COP 5 draws about 5.9 kW. Multiply by your electricity rate per kWh for the hourly cost.
Two honest caveats:
Rated COP is optimistic. Manufacturers test at around 80°F air and 80°F water. On a 60°F morning your real COP will be lower — Department of Energy analysis has put realistic figures closer to the high 3s in cooler conditions.
Run time is much longer. A heat pump delivers heat far more slowly, so while your cost per hour is much lower, you're running many more hours. The savings are still real and substantial — just don't compare hourly rates without comparing hours.
The variable nobody puts in the formula
Everything above calculates the cost of raising your temperature. In practice, most of what you pay for is replacing heat you lost.
An uncovered pool loses heat continuously, and the great majority of that loss is evaporation off the surface. Every gallon that evaporates takes a substantial amount of heat with it.
The factors that drive your real bill, in rough order of impact:
- Whether you use a solar cover. By a wide margin the biggest one.
- Wind exposure. Wind across the surface accelerates evaporation dramatically. A windbreak or fence is a heating upgrade.
- Night-time temperature drop. Cool nights undo a warm day if the pool is open to the sky.
- Your target temperature. Each degree costs more than the last, because a hotter pool loses heat faster.
- Pool size. More gallons, more everything.
- How long your season is.
Six ways to cut the bill
Use a solar cover, every night. Nothing else on this list comes close. It's the difference between heating your pool and heating the atmosphere. See Solar Pool Covers 101 and our post on running a heater and cover together.
Set a temperature and leave it. Holding 84°F costs less than repeatedly letting the pool fall to 70°F and hauling it back up. Cycling is expensive.
Drop your target by two degrees. Most people can't tell 84°F from 86°F in the water. Your bill can.
Block the wind. Fencing, hedging or a privacy screen on the prevailing-wind side pays for itself over a few seasons.
Heat when you'll use it. Don't hold a pool at 86°F through a week nobody swims.
Keep the equipment serviced. A scaled heat exchanger, a dirty filter or a struggling pump all cost you efficiency. Balanced water protects the heater as well as the liner.
Our post on 8 ways to save on swimming pool costs covers the wider running budget.
A sanity check before you buy
Run the numbers before you order, not after. Specifically:
- Calculate your pool's gallons
- Decide your target temperature and typical starting temperature
- Work out the BTUs required
- Divide by your candidate heater's delivered output to get hours
- Multiply by your actual fuel rate
- Ask yourself honestly how many times a season you'll do that
If the answer makes you wince, that's useful information — and it's often the moment people decide either to buy a cover first, or to size up so they're running fewer hours, or to look at a heat pump if their climate supports one. Our pillar guide to heating an above ground pool covers that decision.
The short version
- Gallons × 8.34 × degrees of rise = BTUs needed. Everything starts there.
- Natural gas: heater BTU ÷ 100,000 = therms per hour. Propane: ÷ 91,500 = gallons per hour.
- Raypak Digital units run at 82% thermal efficiency, so multiply rated input by 0.82 for delivered heat.
- Heat pumps: BTU ÷ COP ÷ 3,412 = kilowatts. Cheaper per hour, many more hours.
- Rated COP is measured in warm conditions and will be lower in the real world.
- Most of your bill is replacing evaporation loss, not raising temperature.
- A solar cover is the single biggest cost reduction available to you.
