Pool Heater Calculator
Estimate how long a pool heater could take to reach your target temperature. Enter pool gallons, starting water temperature and heater BTUs to see ideal heating time, hourly temperature rise and the capacity needed for a chosen warm-up period.
How to use this calculator
The tool distinguishes gas fuel-input ratings from heat-pump delivered output. Adjustable efficiency and heat-loss inputs let you compare ratings using the same pool and assumptions, instead of treating every advertised BTU figure as identical heat delivered to the water.
- Enter your pool volume and the starting and target water temperatures.
- Choose gas input, heat-pump output or known heat output, then select or enter a BTU rating.
- Adjust performance and losses, then review heating time and the BTU comparison.
Worked example
A 20,000-gallon pool warmed from 70°F to 85°F needs about 2,502,000 BTUs. A 400,000 BTU/hr gas-input heater at 84% efficiency supplies 336,000 BTU/hr to the water. With no heat loss, the estimated rise is 2.01°F per hour and the warm-up takes about 7.45 hours.
Example inputs illustrate the calculation. Enter your own measurements, product directions and rates to plan your pool.
Turn your result into a plan
Use this estimate to compare warm-up goals, then evaluate fuel or electrical supply, pool surface area, climate, flow and installation requirements. The Heater Operating Cost calculator adds the fuel-price side of the decision using a separate set of energy inputs.
Explore related equipment
Review these product pages as part of your equipment planning. Confirm model, installation and system compatibility before ordering.
Pentair UltraTemp 140 Heat/Cool Heat Pump | 460958
View product details →Frequently asked questions
Does a 400,000 BTU gas heater deliver all of that heat to the pool?
A gas rating generally describes fuel input. Thermal efficiency determines the portion delivered to water. In the worked example, 400,000 multiplied by 84% gives 336,000 BTU/hr of output.
Why might actual heating take longer?
Evaporation, wind, cool air and overnight cooling remove heat. Heat-pump output can also change with conditions. The estimate assumes steady output and the heat loss you enter throughout the warm-up.
Can I compare a gas heater with a heat pump?
Yes, using the appropriate rating basis. Gas input needs efficiency applied; heat-pump output is already delivered heat at its specified conditions. Use performance values appropriate for the equipment and weather.
Does the result choose the right heater for me?
It estimates warm-up behavior. Final sizing needs site and installation information, including surface area, operating goals, climate and manufacturer requirements. Send PSD the pool and equipment details for help reviewing options.
Continue your pool planning
Need help choosing pool equipment?
Send Pool Supply Depot your pool size, calculator results and existing equipment details. We can help review product options and the information to confirm with your installer. Based in Henderson, Nevada, we serve pool owners and pool professionals nationwide.
Pentair Pool and Spa Equipment
Pentair is renowned for its innovative and energy-efficient pool and spa equipment. From pumps to heaters, Pentair offers a range of products designed to enhance your pool experience.
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Hayward is a trusted name in the pool industry, known for its durable and high-performance equipment. Whether you're looking for filtration systems or automation, Hayward has you covered.
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