A swimming pool heat pump is a device that uses a small amount of energy to transfer heat from one location to another. Heat pumps for swimming pools move heat from the outdoors into the water. Unlike gas pool heaters that require natural gas or propane, they use already available heat and transfer it from one place to another, thus utilizing cleaner heat via electricity and producing no carbon monoxide.

Why Use a Heat Pump for Water Heating?

Reason 1: Use Your Pool Year-Round

Swimming pool heat pumps are ideal for use in warmer climates! They are most efficient when heating outdoor air above 50 ºF. Below 50 ºF, the efficiency of a heat pump decreases. In fact, heat pumps work more efficiently the warmer the air temperature gets.

Reason 2: Better Energy Savings

If you want to save on your energy bill, heat pumps for pools offer great value. Imagine a gas heater as a muscle car and a pool heat pump as a bike. A gas heater will heat your pool faster, but at a higher cost. Conversely, a heat pump provides even and consistent heat once it reaches your desired temperature, operating with much less effort. According to the U.S. Department of Energy, running an average swimming pool heat pump year-round at 85 ºF can save you up to $400 annually in energy costs.

Reason 3: Dual Functionality

If you're in the market for a heater, you're likely already invested in making your pool an enjoyable experience. Why not take it a step further? A premium heat pump for swimming pools will not only heat your pool but also cool the water when the weather is excessively hot.

Choosing a Swimming Pool Heat Pump

Swimming pool heat pumps generally cost more upfront than gas pool heaters, but they have significantly lower annual operating costs due to their higher efficiencies. With proper maintenance, heat pump pool heaters often outlast gas heaters, resulting in more savings over time.

When choosing a heat pump pool heater, consider the following factors:

• Size

• Efficiency

• Costs

Sizing a Heat Pump Pool Heater

A trained pool professional should conduct a proper sizing analysis for your specific pool to determine the correct pool heater size.

Sizing a swimming pool heat pump involves several factors. Essentially, a heater is sized based on the pool's surface area and the temperature difference between the pool water and the average air temperatures. Other factors, such as wind exposure, humidity levels, and cool night temperatures, also affect the heating load for outdoor pools. Pools in areas with higher average wind speeds, lower humidity, and cool nights will need a larger heater.

Heat pump pool heaters are rated by Btu output and horsepower (hp). Standard sizes include 3.5 hp/75,000 Btu, 5 hp/100,000 Btu, and 6 hp/125,000 Btu.

To calculate an approximate heater size for an outdoor swimming pool, follow these steps:

1. Determine your desired swimming pool temperature.

2. Determine the average temperature for the coldest month of pool use.

3. Subtract the average temperature for the coldest month from the desired pool temperature to find the temperature rise needed.

4. Calculate the pool surface area in square feet.

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        Use the following formula to determine the Btu/hour output requirement of the heater:

                             Pool Area x Temperature Rise x 12

This formula is based on a 1º to 1-1/4ºF temperature rise per hour and a 3-1/2 mile per hour average wind at the pool surface. For a 1-1/2ºF rise, multiply by 1.5. For a 2ºF rise, multiply by 2.0.

Determining Heat Pump Pool Heater Efficiency

The energy efficiency of heat pump pool heaters is measured by the coefficient of performance (COP). The higher the COP number, the more efficient the heater. The federal test procedure for swimming pool heat pumps sets the test conditions at 80ºF ambient dry bulb, 63% relative humidity, and 80ºF pool water. COPs usually range from 3.0 to 7.0, translating to an efficiency of 300%–700%. This means that for every unit of electricity used to run the compressor, you get 3–7 units of heat from the heat pump.

Estimating Heat Pump Pool Heater Costs and Savings

For an outdoor pool, use the following tables to estimate your annual heat pump pool heater costs and savings compared to using an electric resistance or gas pool heater.

Table 1 estimates annual heat pump pool heating costs by location, water temperature, and with or without using a pool cover.

*Data based on a 1,000 sq. ft. outdoor swimming pool heated with an air-to-water heat pump with an average COP of 5.0 and $0.1301 per kWh.

In comparison to using an electric resistance or gas pool heater with an efficiency of 55% (baseline), Table 2 calculates the savings for each $1000 in annual pool heating costs when using a heat pump pool heater.

Table 2: Comparison of Gas and Electric Pool Heaters' Annual Savings*

*Based on an electric resistance heated pool, which costs $1,000 per year at an electric cost of $.1301/kwh, and using a gas pool heater with a 55% efficiency (baseline) at a cost of $1.09/therm. A seasonal average COP of 5.0 was used to determine heat pump savings.

Installation and Maintenance

The efficiency of your heat pump pool heater can be maximized with proper installation and maintenance. It is best to leave complex maintenance and repair work to a qualified pool professional, who can also install the heater (especially the electric hookup).

To find a maintenance schedule and/or suggestions, consult your owner's manual. Your pool heater most likely needs to be tuned up once a year. Owing to the numerous moving and electrical components, a heat pump pool heater will likely need recurring maintenance from an air conditioning specialist.

Heat pump pool heaters have an extended lifespan of up to ten years when installed and maintained properly.