How long does it take to heat a pool?

With a properly sized heat pump, 2–4 days for a 15–18 °F rise.

Does a solar cover help?

It cuts overnight losses by 50–70%.

Gas heats fast; heat pumps cost less to run in warm weather.

What temperature for a heated pool?

78–82 °F for recreational swimming.

How much does it cost to heat a pool?

Get kWh here, divide by your heat pump's COP and multiply by your rate.

Solar is free to run but weather-dependent; heat pumps are steadier.

Pool heater sizing calculator

Pool size, current and target temperature, hours to heat and losses: you get heat pump output and energy needed.

Heat pump output

39990.3 BTU/h

Heat pump output39990.3 BTU/h
Energy for initial heat-up468.83 kWh
Electricity use at COP 593.77 kWh

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Calculate labour, margin & VAT

How it's calculated (visible formula)

E (kWh) = volume (l) × 4.186 × ΔT ÷ 3600; P = E ÷ hours × (1 + losses); 1 kW = 3,412 BTU/h

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Work out pool volume.
Enter current and target temperatures.
Work out energy to heat that volume.
Divide by the hours you want it done in.
Add losses and pick the heater.

Worked example: 11,840 gal from 64 to 81 °F in 48 h, 20% losses

E = 44,800 l × 4.186 × 9 ÷ 3600 ≈ 469 kWh
469 ÷ 48 × 1.2 ≈ 11.7 kW

→ About 40,000 BTU/h of heat pump output.

Common mistakes

Ignoring losses without a cover.
Expecting rated COP in cool air.
Sizing by surface only, ignoring volume.

Pro tips

Use a cover at night — the biggest saving.
Shield the pool from wind to cut evaporation.
Run heat pumps in the warmest hours.
Maintain temperature rather than reheating from cold each weekend.

From calculation to quote

Add labour, overhead and your margin, and generate the professional PDF.

Create quote Calculate margin & VAT

FAQs

How long does it take to heat a pool?: With a properly sized heat pump, 2–4 days for a 15–18 °F rise.
Does a solar cover help?: It cuts overnight losses by 50–70%.
Gas or heat pump?: Gas heats fast; heat pumps cost less to run in warm weather.
What temperature for a heated pool?: 78–82 °F for recreational swimming.
How much does it cost to heat a pool?: Get kWh here, divide by your heat pump's COP and multiply by your rate.
Heat pump or solar?: Solar is free to run but weather-dependent; heat pumps are steadier.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.