Pool Heater & Heat-Up Time Calculator
Wondering how long your heater needs to run — or whether it’s big enough? Enter your pool volume, the temperature rise you want and your heater’s BTU rating to estimate the heat-up time.
Pool Heater & Heat-Up Time Calculator
Why use the Pool Heater & Heat-Up Time Calculator
Running a heater blind means either a still-cold pool or a nasty gas bill. This shows the hours and energy needed for the exact temperature bump you want.
How to get your numbers
- Volume in gallons.
- Temperature rise = the temperature you want minus the current water temp.
- Heater BTU rating: printed on the unit’s data plate.
Recommended for this job
How to use it
- Enter your pool volume in gallons.
- Enter how many degrees you want to raise the water.
- Pick your heater’s BTU rating (on its data plate).
Frequently asked questions
How long does it take to heat a pool?
It takes about 8.34 BTU to raise one gallon 1°F. A 250,000 BTU heater warms a 20,000-gallon pool roughly 10°F in around 8 hours with a cover on.
Does a pool cover really help heating?
Yes, dramatically. Most heat loss is evaporation from the surface, so a cover can cut heating time and cost by roughly half.
What size pool heater do I need?
For quick recovery, size it to raise your water about 1–1.5°F per hour. Bigger heaters cost more up front but reach temperature far faster.
Gas heater, heat pump, or solar — which is best?
Gas heats fastest and works any weather but costs the most to run; heat pumps are efficient but slow and need warm air; solar is cheapest to run but depends on sun.
How much does it cost to heat a pool?
It depends on fuel price and heater size. Use the BTU figure from this calculator with your gas or electricity rate to estimate the cost per heat-up.
Why won’t my pool get warm?
Common causes are an undersized heater, no cover, windy or cold nights that shed heat faster than you add it, or a heater problem.
What temperature should a pool be?
Most swimmers are comfortable at 78–82°F. Lap swimmers prefer the cooler end; young children and warm-water exercise prefer the warmer end.
