How long to heat a pool?

Roughly volume × 8.34 × degrees of rise ÷ heater BTU/hr. A 250k BTU heater raising 20,000 gal by 10°F takes about 7 hours of ideal run time, more in the cold.

What size heater do I need?

Bigger BTU heats faster. For quick on-demand heating, many size to about 1 BTU/hr per gallon or more; a heat pump is slower but far cheaper to run.

Home › Pool Heater Calculator

Pool Heater Calculator

Enter your pool volume, current and target temperature, and your heater's BTU output to estimate the heat-up time.

Balance your whole pool at once →Enter all your readings on one screen and get an ordered dosing plan — the full Water Report.

How to use it

Enter your volume, current and target water temperature, and your heater's BTU/hr rating.
Plan for the estimate plus ~25% in cool weather.
Use a solar cover to hold the heat and cut both time and cost.

How heat-up time is figured

It takes about 8.34 BTU to raise one gallon of water 1°F. So the energy needed is volume × 8.34 × the temperature rise, and the time is that divided by your heater's BTU/hr output. Real time runs longer because the pool constantly loses heat to the air — especially uncovered and in wind.

Frequently asked questions

How long to heat a pool?: Roughly volume × 8.34 × degrees of rise ÷ heater BTU/hr. A 250k BTU heater raising 20,000 gal by 10°F takes about 7 hours of ideal run time, more in the cold.
What size heater do I need?: Bigger BTU heats faster. For quick on-demand heating, many size to about 1 BTU/hr per gallon or more; a heat pump is slower but far cheaper to run.

Related calculators

Built & reviewed by a working pool-service pro. Target ranges follow CDC MAHC, PHTA, and Taylor guidance. Doses are starting estimates — add a little less than the max, re-test, and confirm against your product label. Educational tool, not a substitute for a water test or professional advice.