Swimming Pool Blog

Heat Pump Sizing Guide

concrete skimmer replacement
by Mark Garcia August 13, 2013

Pool Heat Pump Sizing Guidelines

heat pump sizing guidelines

Heat pumps provide slow, even pool heating by transferring the heat in the air outside to your pool water.

They aren't known for speed, but average about 1-3 degrees increase in the water temperature per day, and can add 20 degrees of temperature rise.

Very cheap to operate, only a few dollars per day, and without burning fossil fuels or emitting carbon monoxide, heat pumps are the choice for eco-friendly pool owners everywhere.

They do have a drawback, besides their slow heating. They lose effectiveness when it's below 50 degrees outside. Warm and humid air is needed to heat the pool water.

Here are the factors to consider when sizing heat pumps for your pool.

Pool Size

Specifically surface area of your pool. Multiply the length x width of your pool - for freeform pools use the longest length and widest width, to calculate your pool surface area. An 18x36' pool would have 18'x36'=648 square feet of surface area. For round pools the formula is pi x radius squared. For a 24' round pool, it's 3.14 x144 = 452 sq. ft.

Here's a chart you can use to see the range of sizes that would be good for the square footage (area) of your pool.


Covered Pools

If you cover the pool consistently, either with a solar blanket of good quality, or an automatic pool cover, you can be in the left hand third of the heat pump size ranges for your size of pool.

Covered pools retain 70% or more of heat put into the pool. In other words, if you plan to use a cover, consistently, then you may be able to install a heat pump of a smaller size.

Sunbelt or Snowbelt Pools

If you live in a mild climate, with annual average temperatures in the 60's, which includes most of the south and west, you can be in the left hand third of the heat pump size ranges for your size pool. For those that live in the upper third of these United States, look to the right hand third of the heat pump size ranges. In other words, if you live in a colder climate, where 50 degree days come early - install a larger heat pump.

Heat pumps still work at lower temperatures, just not as well, when temps reach 50 degrees, BTU output drops by as much as half, and as the temperature gets into the forties, it drops off by half again.

Wind SpeedUS wind speed map

On any uncovered pool, wind is the largest heat thief, stealing your BTU's as it whips across the surface. If your pool area is windy, you may lean towards the larger sizes in the heat pump size ranges for your size pool. Wind blocks such as fences, pool houses or hedges, built on the windward side of the pool, can make a difference.

Average or low wind areas need not consider this perhaps, but others in high wind areas should consider this when sizing a heat pump.


Key Takeaways

What have we learned today?

  1. Heat Pump sizing is by BTU of output
  2. More surface area, and windy and cold areas should use a larger heat pump
  3. Wind is still a Lowdown Heat Thief
  4. Heat pumps heat less in colder temps, at 40 degrees they don't work at all
  5. Heat pumps cost twice as much as a gas heater, but cost 80% less to operate


Thanks for Reading!

Mark Garcia