How much does it cost to heat a pool per month with a heat pump?
A 125,000 BTU/h heat pump with a COP of 5 uses about 7.33 kWh an hour. At an example $0.17 per kWh, running 8 hours a day for 30 days, that is $298.93 a month ($1.25 an hour), or about $149.47 with a cover on when nobody is swimming.
How to work it out
- Per hour: 125,000 BTU/h output ÷ COP 5 = 7.33 kWh × $0.17 per kWh = $1.25
- Per month: $1.25 × 8 hours × 30 days = $298.93 (1,758 kWh)
- Heat-up: 20,000 gal × 8.34 × 12°F (70°F → 82°F) = 2,001,600 BTU ÷ COP 5 = 117 kWh = $19.94
- With a cover: $298.93 × 50% = $149.47 a month
A heat pump’s running cost is easy to work out once you know three numbers: its output, its COP and how long it runs. The hours are the slippery part, so this page starts from 8 hours a day and shows what more or fewer does to the bill.
Adjust for your project
- Energy used per month
- 1,758 kWh
- Cost per hour of running
- $1.25
- Energy per hour of running
- 7.33 kWh
- Cost of one heat-up (no losses)
- $19.94
- Energy for one heat-up
- 117 kWh
- Per month with a cover (DOE’s low end: 50% less)
- $149.47
- With a cover on whenever nobody is swimming, the DOE puts the heating savings at 50–70%: about $149.47 a month at 50%, and as little as $89.68 at 70%.
- A heat pump’s COP is measured at 80°F air. On cool days both its output and its COP fall, so it runs longer and costs more per degree; the DOE says they work efficiently only above about 45–50°F.
125,000 BTU/h heat pump at $0.17/kWh, by hours 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 | $74.73 | 440 kWh | $37.37 |
| 4 h | $149.47 | 879 kWh | $74.73 |
| 6 h | $224.20 | 1,319 kWh | $112.10 |
| 8 h | $298.93 | 1,758 kWh | $149.47 |
| 12 h | $448.40 | 2,638 kWh | $224.20 |
| 24 h | $896.80 | 5,275 kWh | $448.40 |
Where the $299 comes from
The heat pump is a 6 hp, 125,000 BTU/h model, the largest of the DOE’s standard sizes. A COP of 5 means it moves five units of heat into the water for each unit of electricity, so it draws 125,000 ÷ 5 = 25,000 BTU of electricity an hour. At 3,412 BTU per kWh that is 7.33 kWh, and at $0.17 per kWh, $1.25 for every hour the compressor runs. Eight hours a day for 30 days is 240 hours, or 1,758 kWh.
- Hours are the whole story. In a warm month with a cover, a heat pump holding 82°F might run 3–4 hours a day; uncovered in spring, it can run around the clock. At 24 hours a day this same unit costs about $897 a month.
- COP moves with the weather. The DOE puts typical COPs between 3 and 7, measured in 80°F air. At COP 3, the same 8 hours cost about $498 a month.
- One heat-up from 70°F to 82°F on 20,000 gallons is about 2 million BTU of heat, roughly 117 kWh at COP 5, or about $20 at this rate, before losses.
A cover is the biggest lever: the DOE puts heating savings at 50–70%, so about $150 a month here at the conservative end. To check whether the unit is big enough in the first place, run what size pool heater for 20,000 gallons; for what a heater adds per degree and per hour, see how long to heat a pool 10 degrees.
Different size? Use the full Pool Heating Cost Calculator.
What you’ll need
- 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) - 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)
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
What does a heat pump cost per month running 4 hours a day?
About $149.47 (879 kWh) for a 125,000 BTU/h heat pump at COP 5 and $0.17 per kWh.
What does a 250,000 BTU gas pool heater cost per hour?
About $3.75 at an example $1.50 per therm: it burns 2.5 therms an hour at full fire.
What does a 100,000 BTU heat pump cost to run per month?
About $239.15 at 8 hours a day, COP 5 and $0.17 per kWh ($1.00 an hour).
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.