Pool Heating Cost Calculator (gas, heat pump, electric, cover savings)

Cost pool heating per month: the same heat priced as gas therms, heat pump kWh and electric resistance, from your own fuel rates, with the heat-up run and a cover saving you set.

How this is calculated

Two steps, kept apart on purpose. First the pool's heat demand in BTU, which is the same whatever burns to supply it. Then that demand is divided by each heater's own conversion, which is the only thing that differs between gas, a heat pump and an element.

HEAT DEMAND (BTU delivered into the water)
run time     dailyBtu = heaterOutput(BTU/hr) x runHours/day
estimate     dailyBtu = area(sq ft) x (water - air)(°F) x k x heldHours/day
             k = BTU/hr per sq ft per °F   [your number, not a sourced constant]
cover        dailyBtu x (1 - coverHours/24 x coverCut%)
monthly      dailyBtu x 365/12
season       monthly x seasonMonths

ONE-OFF HEAT-UP
heatUpBtu    = volume(gal) x 8.34 lb/gal x 1 BTU per lb per °F x rise(°F)

COST PER HEATER
gas          therms = BTU / efficiency / 100,000      cost = therms x price/therm
heat pump    kWh    = BTU / COP / 3,412               cost = kWh x price/kWh
electric     kWh    = BTU / efficiency / 3,412        cost = kWh x price/kWh

Worked example. A 400,000 BTU/hr heater firing 5 hours a day delivers 2,000,000 BTU a day, or 60,833,333 BTU in an average month (365/12 = 30.4 days). At 82% that is 741.87 therms of gas; at a COP of 3.5 it is 5,094 kWh; through a resistance element it is 17,829 kWh. Type in $1.50 a therm and $0.18 a kWh, your own numbers rather than ours, and the same heat costs $1,112.80 on gas, $916.93 on the heat pump and $3,209.26 on the element. The spread is the point: the heat is identical, the bill is not.

Where every constant comes from. 1 therm = 100,000 BTU and 1 kWh = 3,412 BTU are the U.S. Energy Information Administration's own definitions, and a BTU is defined there as the heat that raises one pound of liquid water by one degree Fahrenheit. 8.34 lb/gal falls out of the USGS water density table, which gives 62.366 lb per cubic foot at 60°F, divided by the 7.48 gallons in a cubic foot. Our pool heater BTU calculator rounds the same figure to 8.33, the value nearer pool temperature; the two differ by less than 0.2% and neither is wrong.

The two efficiency defaults are legal floors, not market averages. 82% is the minimum thermal efficiency federal rules require of a gas-fired pool heater made since April 2013 (10 CFR 430.32(k)(1)). A COP of 3.5 is the minimum California requires of a heat pump pool heater made since March 2003 (Cal. Code Regs. tit. 20 section 1605.3), measured as the average of its standard and low temperature ratings. Your equipment is probably better than both, and a heat pump in cold air is often worse than its plate, so both sit in editable boxes.

Two numbers here are deliberately not asserted. The surface loss coefficient and the cover's percentage cut are your inputs, not our claims. The much-quoted "a pool cover saves 50% to 70% of heating costs" line is attributed to the U.S. Department of Energy's Energy Saver pool cover page; that page returned a 404 on energy.gov when we checked it on 11 September 2026, so we will not repeat the figure as fact. The tool ships a neutral 50% in an editable box, applies it only for the hours you say the cover is on, and shows you the arithmetic.

What this tool is not. It does not size a heater and it never recommends one. Sizing is a different question with a different formula, and it lives in the pool heater BTU calculator. The circulation pump's electricity is a separate line on the same meter, so the pool pump energy cost calculator prices that, and the variable-speed pump savings calculator prices the upgrade that cuts it.

Everything runs in your browser. No account, no email gate, nothing stored or sent.

What this prices, and what it deliberately does not

A pool heater raises two separate questions, and mixing them is how most calculators go wrong. How big a heater do I need is a sizing question, answered from surface area and the temperature rise you want. What does it cost to run is an energy question, answered from the heat you deliver and what your fuel costs. This page answers the second one only. The first belongs to the pool heater BTU calculator, and nothing here recommends a heater size, a brand or a model.

The structure is deliberately plain: work out the heat the pool takes in BTU, then divide that heat by each heater’s own conversion. Gas buys therms at a thermal efficiency. A heat pump buys kilowatt-hours at a coefficient of performance. An electric element buys kilowatt-hours at essentially one to one. All three are shown against the same heat, every time, because the comparison only means something when the heat on both sides is identical.

Every fuel price starts empty

There is no national pool heating cost, and the tool will not invent one. A therm in one state costs what two cost in another, and residential electricity rates vary by a factor of four across US states alone, before any market outside the US is considered. So both price boxes ship blank and stay blank until you type the unit rate off your own bill.

One thing to leave out when you do: the standing charge, supply charge or meter fee. That is a fixed daily cost of being connected, payable on days the heater never fires, so it is not part of what the heat costs and including it would distort every comparison on the page.

Run hours beat any loss model

The default mode asks what your heater actually did: its output in BTU per hour, and the hours a day it fires. That is a measurement, not a model, and it is the number to quote from.

The second mode estimates the demand from the pool itself, using water surface area, the water-to-air temperature difference and a surface loss coefficient. It is useful for scoping a pool you have not metered, and we ship it with an explicit warning attached, because the coefficient is the weakest number on the page. Figures between about 5 and 10 BTU per hour per square foot per degree F circulate widely for an uncovered outdoor pool, and none of them traces back to a regulator, a standards body or a published measurement we could verify. Wind, humidity, shade and a clear night sky move the real figure more than the rounding does. It sits in an editable box, labelled as your number rather than ours.

The cover saving is scaled by the hours it is on

A cover only saves heat while it is actually on the water, so a flat percentage applied to a whole month is wrong on its face. This tool asks two things: how many hours a day the cover is on, and what percentage of the loss you believe it cuts while it is there. Twelve hours at a 50% cut is a 25% reduction across the day, not 50%.

The percentage itself is your input and not our assertion. The widely repeated “a pool cover saves 50% to 70% of heating costs” line is attributed to the US Department of Energy’s Energy Saver pool cover page, and that page returned a 404 on energy.gov when we checked it on 11 September 2026. We will not launder an unverifiable figure into a calculator, so the box ships at a neutral 50% with that explanation attached.

One coupled effect worth flagging: if you measured your run hours on a pool that was already being covered, the saving is baked into those hours. Adding cover hours on top counts it twice. The page says so inline when both are filled in.

The heat-up is a separate, one-off bill

Bringing a cold pool up to temperature in spring is not part of the monthly running cost, and folding it in would overstate every month after the first. Enter a volume and a starting temperature and it is priced as its own line, from the textbook energy chain: gallons times 8.34 pounds per gallon times one BTU per pound per degree F times the rise. If you do not know the gallons, the pool volume calculator works them out from the shape and depths.

Where the rest of the pad’s energy goes

Heating is usually the biggest line on a heated pool’s power bill, but it is never the only one. The circulation pump runs on the same meter, often for more hours a day than the heater, and the pool pump energy cost calculator prices that side with published US, UK and Australian rates built in. If the pump turns out to be the bigger number, the variable-speed pump savings calculator prices the upgrade against its payback period, which is a far cheaper lever than changing a heater.

Switch units freely. The tool opens in US units and toggles to square metres, litres and degrees Celsius, and the gas price accepts either a price per therm or a price per kilowatt-hour of gas, which is how most metric-market bills read. Currency is formatted, never converted: the number you type is the number that is used.

Frequently asked questions

How much does it cost to heat a swimming pool per month?

It depends far more on your fuel price than on your pool, which is why this calculator asks for the price rather than assuming one. Work it from the heat: a 400,000 BTU/hr heater firing 5 hours a day delivers 2,000,000 BTU a day, or about 60,833,333 BTU in an average month (365/12 = 30.4 days). At 82% thermal efficiency that is 741.9 therms of gas; through a heat pump at a COP of 3.5 it is 5,094 kWh; through an electric element it is 17,829 kWh. Multiply each by your own unit rate and you have three very different bills for exactly the same warm water.

Is a heat pump really cheaper to run than a gas pool heater?

Usually, and the reason is arithmetic rather than marketing. A gas heater delivers less heat than the fuel contains, because some goes up the flue: at 82% thermal efficiency you buy 100 units of gas and get 82 into the water. A heat pump moves heat instead of making it, so a COP of 3.5 means 1 unit of electricity delivers 3.5 units of heat. Whether that wins on your bill depends on the gap between your gas and electricity prices, which is why this tool prices both against the same heat and tells you which one is cheaper at your rates. Two honest caveats: a heat pump loses output and COP as the air cools, so it is weakest exactly when you want it most, and it takes much longer to raise the temperature than a gas heater of the same nominal size.

How much does a pool cover actually save on heating?

We do not assert a figure, and that is deliberate. The "50% to 70%" number every pool site quotes is attributed to the U.S. Department of Energy's Energy Saver pool cover page, and that page returned a 404 on energy.gov when we checked it on 11 September 2026, so there is nothing live to cite. Under this site's cite-or-omit rule the saving is your input, not our claim. What the tool does contribute is the structure most cover calculators get wrong: a cover only saves while it is on, so the reduction is scaled by the hours a day you actually use it. Twelve hours at a 50% cut is a 25% saving across the day, not 50%.

Does this tell me what size pool heater to buy?

No, and it should not. Sizing and running cost are two different questions with two different formulas, and a calculator that answers both in one number is quietly mixing them. Sizing is driven by surface area and the temperature rise you want; running cost is driven by the heat you deliver and what your fuel costs. Size the unit in the pool heater BTU calculator, then bring the output figure back here to see what running it will cost.

Why does the tool ask for run hours instead of working the heat out for me?

Because measured run hours are the only input on this page that is not a model. Surface heat loss depends on wind, humidity, shade, night sky and the difference between water and air, and the coefficients that circulate for it (roughly 5 to 10 BTU per hour per square foot per degree F) do not trace back to any regulator, standards body or published measurement we could find. So the run-time mode is the default and the estimate mode ships with the coefficient in an editable box and a warning attached. If you have a run-hour meter or a heater with an hours counter, use it and the whole question of loss coefficients disappears.

Should the standing charge or the meter fee be in this number?

No. A standing charge is a fixed daily fee for being connected and you pay it on a day the heater never fires, so folding it into the heating cost overstates what the heat costs and makes every comparison on this page wrong. Enter the unit rate only: the price per therm or per kWh of the energy you actually consume. The same rule applies on the pool pump energy cost calculator, and for the same reason.

Sources

Glossary: British thermal unit, defined as the quantity of heat required to raise the temperature of 1 pound of liquid water by 1 degree Fahrenheit. U.S. Energy Information Administration. Retrieved Sep 11, 2026.
Glossary: Therm, defined as one hundred thousand (100,000) Btu. U.S. Energy Information Administration. Retrieved Sep 11, 2026.
Energy conversion calculators: 1 kilowatthour = 3,412 Btu (standard conversion factor). U.S. Energy Information Administration. Retrieved Sep 11, 2026.
Water Density: water weighs 62.366 pounds per cubic foot at 60 degrees F, which is 8.34 pounds per US gallon at 7.48 gallons per cubic foot. U.S. Geological Survey, Water Science School. Retrieved Sep 11, 2026.
10 CFR 430.32(k)(1): gas-fired pool heaters manufactured on and after April 16, 2013 and before May 30, 2028 shall have a thermal efficiency not less than 82%. Electronic Code of Federal Regulations (eCFR). Retrieved Sep 11, 2026.
Cal. Code Regs. tit. 20 section 1605.3: for heat pump pool heaters manufactured on or after March 1, 2003, the average of the COP at Standard Temperature Rating and the COP at Low Temperature Rating shall be not less than 3.5. California Code of Regulations, via Cornell Legal Information Institute. Retrieved Sep 11, 2026.

How we choose and check our formulas