Swimming Pool Blog

An In-Depth Look at Pool Heat Pumps

An In-Depth Look at Pool Heat Pumps

in depth look at pool heat pumps

by Alicia Harris, September 5, 2018

An In-Depth Look at Pool Heat Pumps

Unlike natural gas or propane pool heaters, a pool heat pump can't generate its own heat. This might sound strange at first. How else is a heat pump supposed to warm up your pool water?!

It's simple! Heat pumps draw heat from the surrounding air and transfer it to the pool. Being able to draw heat from the surrounding air makes heat pumps more energy efficient than other pool heaters that use gas or electricity to generate their own heat. Let's take a closer look, shall we?

How Does a Pool Heat Pump Work?

It's easiest to compare a heat pump to an air conditioner. Both use electricity, they look very similar, and they also have many of the same internal components. Much like an AC unit for your home, a pool heat pump simply transfers heat from one place to another.

A fan draws warm ambient air across an evaporator coil filled with cool liquid refrigerant. Heat from the air is absorbed by the liquid, which is converted into gas vapor as it heats up. This warm, low pressure gas then goes through a compressor to increase its pressure and temperature. From the compressor, this hot, high pressure vapor makes its way to the condenser.

The hot vapor makes its way through the condenser coil, and its heat energy is transferred to pool water passing over the coil. As the refrigerant loses heat energy, it is converted back into a liquid state. Now a high pressure liquid, the refrigerant then passes through an expansion valve to reduce pressure and lower its temperature. The cooled liquid refrigerant then returns to the evaporator, so the process can begin again. The fan continues to draw warm air across the evaporator while blowing cool air out the top of the unit. At the same time, the heat pump pulls a continuous stream of cool water across the condenser coil, and warm water is returned to the pool.

pool heat pump infographic

Since heat pumps pull warmth from the surrounding air, they will only work properly above 50 degrees Fahrenheit. Because of the way a heat pump works, some models are designed to heat up OR cool down the water, depending on the time of year. Other types are set up to only be water chillers instead of water heaters. Heat-cool pumps are especially popular in warmer climates; they can offer cooler water temperatures during the heat of summer, or they can extend pool season by several months during spring and fall.

What Size of Pool Heat Pump Do I Need?

You'll need to consider pool size and the desired temperature change when selecting a heat pump for your swimming pool. Other factors such as the average air temperature, humidity and wind speeds will also influence a heat pump's ability to warm the pool water. Figuring on a temperature increase of 1-1.25 degrees per hour, you can use the following equation to get an approximate heat pump BTU requirement:

(Surface Area) x (Temperature Increase) x 12 = (Minimum BTU Needed)

For example, we'll use a rectangular pool 14 ft. wide by 28 ft. long. During the coldest month of use, the pool owner wants to increase the water temperature by around 20 degrees Fahrenheit.

(14 x 28) x 20 x 12 = 94,000+ BTU

If you happen to know the volume of your pool in gallons, you can also follow this general guideline for heat pump BTUs:

Pool Volume Heat Output
10,000 gal. 50,000 BTU
15,000 gal. 90,000 BTU
20,000 gal. 120,000 BTU
25,000 gal. 140,000 BTU

Heat pumps max out around 135,000 to 150,000 BTU, so larger pools will take longer to heat. It's important to purchase a properly sized unit in order to maximize energy savings. Using a solar pool cover can also help reduce heat loss and boost efficiency.

How Does a Heat Pump Compare to a Gas Pool Heater?

Pool heat pumps have several advantages and disadvantages compared to natural gas or propane pool heaters.

Pool Heater Heat Pump
Pros: Works well in any temperature. Pros: Environmentally friendly: energy efficient and no emissions.
Lowest purchase cost. Lowest operating cost (electricity). Save up to 75% vs. gas heaters.
Can heat water quickly. No need for gas line installation.
Cons: Gas line installation required. Cons: Highest purchase cost.
Highest annual operating cost (fuel). Doesn't work well below 50 degrees (F).
More moving parts to replace. Large pools over 30,000 gallons won't heat up as quickly.

Is one better than the other for keeping your pool water warm? Not necessarily. Each one has its own merits! Before purchasing a heat pump or gas heater for your pool, look carefully at the pros and cons to determine which will work the best for you. Price, climate, operating costs and installation difficulty should all play a role in your decision.


Have more questions? Give Pool Center a call! Our pool experts are here to answer all of your pool heating questions. With more than 30 styles and multiple sizes of pool heaters and heat pumps in stock, we're sure to have exactly what you're looking for.