Pool Heat Pump Size Calculator

Heater makers use a simple rule: BTU per hour = pool surface area in sq ft x the temperature rise you want in F x 12. A 16 x 32 pool kept 15 F above the air needs about 92,000 BTU. Also check the maker's maximum pool size in gallons.

Divide the BTU rating by COP x 3,412 to get kW, then multiply by your rate. A 100,000 BTU unit at COP 6.4 draws about 4.6 kW, about $0.79 an hour at the US average of 17.3 cents. COP drops in cooler air, so spring and fall hours cost more.

Most of a pool's heat escapes from the surface through evaporation and wind. That is why the sizing rule uses surface area, and why a solar cover is the cheapest way to cut heating cost.

The large in-ground units in our list are 230V or 240V and need a dedicated circuit. A few units up to about 30,000 BTU run on 120V for small above-ground pools.

Surface area x average depth x 7.48. A 16 x 32 pool with a 5 ft average depth holds 512 x 5 x 7.48, about 19,100 gallons. A 15 ft round pool 4 ft deep holds 177 x 4 x 7.48, about 5,300 gallons.

Your target water temperature minus the average air temperature in the coolest month you plan to swim. If you want 82 F water and that month averages 67 F, use a 15 F rise. A longer season means a bigger rise and a bigger heat pump.

kW x hours x your rate. The 65,000 BTU VARPOOLFAYE inverter at COP 6.6 draws 65,000 / (6.6 x 3,412), about 2.9 kW, so 8 hours uses about 23 kWh, about $4.00 a day at 17.3 cents. Fewer hours with a solar cover means a smaller bill.

Not in the way an air conditioner can. A bigger unit heats faster and runs fewer hours, and at the same COP the energy to hold the temperature is about the same. The costs are a higher purchase price and a larger circuit.

A solar heater has almost no running cost but depends on sun and roof space; the Department of Energy says the collector area should equal 50 to 100 percent of the pool's surface area. A heat pump heats on cloudy days and at night, and costs electricity to run. Many owners in sunny climates start with a cover and solar, and add a heat pump for the shoulder seasons.

Outdoors on a level pad, with the clearance around the coil the maker lists so it can pull in air. It is plumbed after the filter and before any chlorinator, so concentrated chlorine does not pass through the heat exchanger. The 230V and 240V units need a dedicated circuit.