Size a Pool Heater - Heat Pump

Choosing the right size pool heater is essential for maintaining the perfect swimming temperature without overspending on energy bills. Whether you're heating a backyard pool or a commercial spa, properly sizing your heater ensures faster heat-up times, longer equipment life, and greater energy efficiency. Use our expert sizing guide to find the ideal heater for your pool’s volume, location, and usage habits—so you can enjoy warm water when it matters most.

Basic Principles for Sizing Heat Pump

Size at 4 BTU's per gallon of water

• To heat a pool in normal summer conditions when the ambient air temperature average is 70°F in a 24 hour period. For example, if your swimming pool is 10,000 gallons then you should purchase a heat pump with a minimum of 40,000 BTU's.

Size at 5 BTU's per gallon of water

• To heat a pool in spring and fall conditions when the ambient air temperature average is 60°F in a 24 hour period.

Swimming Pool Sizing Chart

Please Note: We recommend the use of a pool cover in addition to your heat pump. Keeping the cover on your swimming pool during the nighttime hours will help prevent heat loss and chemical dissipation.

Unlike gas pool heaters, heat pump pool heaters are designed for steady, long-term operation rather than rapid temperature increases. They work by drawing in ambient air and transferring heat to the pool water, making them highly energy-efficient but slower to heat. For best results, a heat pump should be left on continuously or set to maintain a consistent temperature over time. If you’re looking to quickly raise your pool’s temperature just before swimming, a heat pump may not be the ideal solution—instead, consider a gas heater for faster, on-demand performance.