Pool heating cost calculator: what does it cost to heat a pool?
Pick the heater, enter its rating and your energy price, then how many hours a day it runs. You get the cost per hour, per month and for one heat-up of the pool, and what a cover takes off.
Enter your measurements
- Energy used per month
- 600 therms
- Cost per hour of running
- $3.75
- Energy per hour of running
- 2.5 therms
- Cost of one heat-up (no losses)
- $51.87
- Energy for one heat-up
- 34.6 therms
- Per month with a cover (DOE’s low end: 50% less)
- $450.00
Per hour: 250,000 BTU/h = 2.5 therms × $1.50 per therm = $3.75
Per month: $3.75 × 8 hours × 30 days = $900.00 (600 therms)
Heat-up: 20,000 gal × 8.34 × 17°F (65°F → 82°F) = 2,835,600 BTU ÷ 82% efficiency = 34.6 therms = $51.87
With a cover: $900.00 × 50% = $450.00 a month
- With a cover on whenever nobody is swimming, the DOE puts the heating savings at 50–70%: about $450.00 a month at 50%, and as little as $270.00 at 70%.
Quick answers for common sizes
| Example | Answer |
|---|---|
| What a heat pump pool heater costs per month | $298.93 |
Monthly cost by hours of running a day
| Hours a day | Heating cost per month | Energy used per month | Per month with a cover (DOE’s low end: 50% less) |
|---|---|---|---|
| 2 h | $225.00 | 150 therms | $112.50 |
| 4 h | $450.00 | 300 therms | $225.00 |
| 6 h | $675.00 | 450 therms | $337.50 |
| 8 h | $900.00 | 600 therms | $450.00 |
| 12 h | $1,350.00 | 900 therms | $675.00 |
| 24 h | $2,700.00 | 1,800 therms | $1,350.00 |
Pool heating cost comes down to three numbers: how much fuel the heater burns in an hour, what that fuel costs on your bill, and how many hours it runs. The first comes from the label, the second from your bill, and the third is the one people guess wrong, so the calculator also prices a single heat-up, which doesn’t depend on run time at all.
How the pool heating cost calculator works
- Gas and propane heaters are rated by fuel input. A 250,000 BTU/h heater burns 2.5 therms of natural gas an hour (1 therm = 100,000 BTU), or about 2.7 gallons of propane (about 91,452 BTU per gallon, EIA), at full fire.
- Heat pumps are rated by heat output. Divide by the COP to get the electricity: a 125,000 BTU/h heat pump at COP 5 draws 25,000 BTU of electricity an hour, which is 7.3 kWh (1 kWh = 3,412 BTU).
- Electric resistance heaters turn each kWh into 3,412 BTU, so their output and input are the same.
- One heat-up is the heat the water needs (gallons × 8.34 × °F of rise) divided by the efficiency or COP, priced at your rate. It assumes no losses, so it’s the floor.
gas: therms per hour = BTU/h rating ÷ 100,000 propane: gallons per hour = BTU/h rating ÷ 91,452 heat pump: kWh per hour = BTU/h output ÷ COP ÷ 3,412 electric: kWh per hour = BTU/h ÷ 3,412 monthly cost = cost per hour × hours a day × days one heat-up = gallons × 8.34 × °F rise ÷ (efficiency or COP), in fuel units × price
Typical figures to start from
| Heater | Rating | Fuel per hour at full output | Heat into the water |
|---|---|---|---|
| Natural gas, 82% | 250,000 BTU/h | 2.5 therms | 205,000 BTU/h |
| Propane, 82% | 250,000 BTU/h | 2.73 gal | 205,000 BTU/h |
| Heat pump, COP 5 | 125,000 BTU/h | 7.33 kWh | 125,000 BTU/h |
| Heat pump, COP 3 | 125,000 BTU/h | 12.2 kWh | 125,000 BTU/h |
| Electric resistance | 11 kW | 11 kWh | 37,500 BTU/h |
Per unit of heat in the water, a heat pump at COP 5 uses a fifth of the electricity of a resistance heater, which is why heat pumps dominate where the weather is mild. Gas costs more per degree in most places but heats far faster and doesn’t care how cold the air is. The pool heater vs heat pump guide goes through the trade-off; what a heat pump pool heater costs per month works one through with real hours.
Ways to cut the bill
- Cover the pool. The DOE puts the heating savings from a pool cover at 50–70%, because evaporation is by far the biggest heat loss. The calculator uses 50% to stay conservative. Size one with the solar cover calculator.
- Turn it down a degree or two. The DOE estimates each degree of extra pool temperature costs 10–30% more energy. 80°F instead of 82°F is a real saving.
- Heat for the days you swim. A gas heater can bring the pool up for a weekend; heating it all week for two swims costs five days of losses for nothing.
- Replace an old gas heater with a high-efficiency one. The DOE’s formula for the saving is current yearly cost × [1 − (current efficiency ÷ new efficiency)]. Going from 82% to 95% saves about 14%.
For the whole picture (pump, chemicals and heat), see pool running costs and the pool cost per month calculator. The pump’s share alone is on the pool pump cost calculator.
What you’ll need
- Solar cover (bubble cover)Mid-range price
The cheapest heating upgrade there is: cuts evaporation and holds heat in overnight. Buy the size up and trim it.
See options on Amazon (opens in a new tab) - Solar cover reelMid-range price
A cover that is a pain to take off doesn’t go back on. A reel makes it a one-person, two-minute job.
See options on Amazon (opens in a new tab) - Heat pump pool heaterPremium price
Much cheaper to run than gas in mild weather, but slower, and output drops as the air gets cooler.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How much does a heat pump pool heater cost to run per hour?
Divide its BTU/h output by the COP and by 3,412 to get kWh, then multiply by your rate. A 125,000 BTU/h heat pump at COP 5 uses about 7.3 kWh an hour; at an example $0.17 per kWh that is about $1.25. More detail on heat pump pool heater cost per month.
How many therms does a pool heater use per hour?
Its BTU/h input rating divided by 100,000. A 400,000 BTU/h gas heater burns 4 therms an hour at full fire; a 250,000 BTU/h heater, 2.5 therms.
Is it cheaper to heat a pool with propane or natural gas?
Compare price per BTU. A therm of natural gas is 100,000 BTU and a gallon of propane about 91,452 BTU, so propane is cheaper only if a gallon costs less than about 0.91 times a therm. In most areas it costs more.
Does a pool cover really cut heating costs in half?
The DOE and ENERGY STAR put the savings at 50–70%, because most heat leaves through evaporation and a cover stops most of it. You only get it if the cover is on whenever the pool isn’t in use; the calculator uses the 50% end.
Why is my heating bill higher than the calculator says?
Usually the hours: in cool or windy weather a heater runs much longer to hold temperature, and a heat pump’s COP and output drop below their 80°F ratings. Check run time on the heater’s display or read the meter for a few days.
Related guides
Sources
- US EIA — British thermal units (Btu) (opens in a new tab) — 1 therm of natural gas = 100,000 Btu; 1 gallon of propane ≈ 91,452 Btu; 1 kWh = 3,412 Btu.
- US DOE Energy Saver — Heat pump swimming pool heaters (archived) (opens in a new tab) — COPs usually range from 3.0 to 7.0; rated at 80°F air; work efficiently above about 45–50°F.
- US DOE Energy Saver — Gas swimming pool heaters (archived) (opens in a new tab) — Gas heaters from 75,000 to 450,000 Btu; some are 89%–95% efficient. Savings from a more efficient heater: current annual cost × [1 − (current efficiency ÷ new efficiency)].
- ENERGY STAR — Pool pumps (pool heating notes) (opens in a new tab) — Federal minimum gas pool heater efficiency 82%; covers save 50–70% on heating.
- US DOE Energy Saver — Swimming pool covers (archived) (opens in a new tab) — Covers cut pool heating costs by 50%–70%; evaporation is by far the largest source of energy loss.
- US DOE Energy Saver — Managing swimming pool temperature (archived) (opens in a new tab) — Each degree of extra pool temperature costs 10%–30% more energy.