How Does a Pool Heat Pump Work

backyard swimming pool

Charlie Hardcastle

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If you’re looking for an energy-efficient pump for your pool, a pool heat pump might be the best choice for you. Heat pumps are not a new invention. The technology that is used in this equipment is also used in air conditioners, water coolers, and refrigerators. 

In the simplest terms, the heat pump works like a reverse air conditioner. It transfers heat from the air into the water. The considerable advantage of such a solution is the fact that there is no need to create heat from nothing. The pump’s job is to move it from one place to another. For this reason, pool heat pumps are considered to be more efficient in saving energy.

How Do Pool Heat Pumps Work?

A pump heat works by drawing the hot air with a fan and then circulating it through an outer evaporator air coil. Within the evaporator coil, there is a liquid refrigerant, and its job is to absorb the heat and transform it into gas.

The next thing that takes place is the transfer of warm gas to the compressor. In the compressor, the temperature of the gas increases, which creates a very hot gas that then gets to the heat exchanger condenser. 

The pool water is in circulation, and first, it passes through the filter to be transferred to the pump’s water heater. Next, water from the pool and hot gas meet in the heat exchanger. This is the place where the heat is transferred from gas to water. The water’s temperature rises anywhere from 3 to 5 degrees. This water is then transferred back to the pool, and the whole process takes place all over again. 

The fact that heat pumps do not produce the heat itself, but only transfer it, is a great benefit but also something to be mindful of when deciding on purchasing the pump. Its efficiency is the highest when the temperatures outside oscillate around 45ºF–50ºF. This does not usually present itself as an issue due to the fact that most people use their pools on warmer days. 

Regardless of that, pool heat pumps use more energy to heat the water when it’s cooler outside, and it is worth remembering.

Principle of Operation

It is beneficial to illustrate how the heat pump works with more detail. Here’s how this device operates from a technical standpoint.

The electrical energy powers the compressor in the pump. The compressor sucks gas that is located in the liquid-filled evaporator tube. This process is what is causing the cooling effect. The gas absorbs the heat that is coming from the air outside of the evaporator tubes. 

The gas is squeezed in the compressor, where its temperature rises to 200° F (93° C). In this instant, there are five units of heat added to the gas. The hot gas travels through the condenser coil. The water from the pool picks up the heat from the Freon, cooling it down until it is changed into a warm liquid again.   

The warm liquid goes through a valve where it drops in pressure and expands. Now it is a cold liquid, which then reaches the evaporator to repeat the whole process all over again.


The pool heat pumps are utilized to heat water in on ground, in ground, and above ground pools, as well as hot tubs, spas, and swim spas. Compared to the air conditioner, which can move three units of heat from your space with one unit of electricity, pool heat pumps can move even four and more units of heat from the air. That equals even seven units of heat transferred to your pool water.

How to Choose a Pool Heat Pump?

There are a few parameters worth considering when choosing the right pool heat pump. These factors are the size, efficiency, and costs of a device.

Of course, we can find other solutions for pools, for example, gas pool heaters. Although the heat pump is more expensive, its annual costs of operation are lower, which can make a big difference. Heat pumps are usually the more efficient choice than other options, like gas pumps; therefore, they might be worth the investment.

Size of the Heat Pump

Of course, to get the best possible results, you have to choose the right heat pump size for your pool. This is a task for a professional who will be able to perform the correct sizing analysis and pinpoint the proper device for your specific needs. 

There are a lot of factors that influence how the pump will perform. The size of a heat pump is selected by taking into account the surface area of the pool, as well as the average air temperatures. 

With outdoor pools, it is also significant to think about the exposure to wind, humidity levels, and the differences between the temperatures during the day and night. Taking all these factors into account, we can determine the size of the pump. With a higher average speed of winds and cooler temperatures, a bigger heater would be the right one. 

There are heat pumps with different Btu output and horsepower (hp) parameters. The most common ones are 3.5 hp/75,000 Btu, 5 hp/100,000 Btu, and 6 hp/125,000 Btu.

Here are some steps you can take to determine the right size of the pump for your pool.

  1. Determine the desired water temperature.
  2. Determine the average temperature in the coldest month you plan to use the pool.
  3. Subtract the average temperature in the coldest month from the desired temperature of water in the pool. This will be the temperature rise that your pump should achieve.
  4. Calculate the pool surface area in square feet.
  5. Apply the formula Pool area x Temperature rise x 12 to determine the heater’s Btu/hour output requirement. 

The formula for calculating the size of the heat pump is based on the objectives 1º to 1-1/4ºF temperature rise per hour and a 3-1/2 mile per hour average wind speed.

Efficiency of the Heat Pump

The device’s efficiency can be measured with something called the coefficient of performance (COP). The general rule is that the higher the COP, the more efficient the pump is. 

You will find heat pumps with COPs usually varying between 3.0 to 7.0, which equals the efficiency of 300% to 700%. This simply translates to the fact that the pump will transfer from three to seven units of heat for every electricity unit.


As we mentioned earlier, the upfront purchasing costs of the pool heat pump are usually more significant than the costs of purchasing the gas pump. This, however, does not mean that the heat pumps are not a cost-effective solution.
Annually, you can save up with the heat pump, which is more energy-efficient than other pumps. Here you can see the costs of heat pumps operating in different parts of the country.

Installation and Maintenance

Adequate installation and maintenance of the pump can ensure us with the long-running equipment. Similarly to calculating the right size of a heat pump, installation of it is also something that we should leave to the professionals. 

In the owner’s manual, you can find all the information about the maintenance schedule. It is best to do regular checkups and servicing, for example, by the air conditioning technician. Well-maintained pumps can be efficient for ten years and more.

Advantages and Disadvantages of Heat Pumps

Before deciding on one solution, it is best to acquire all the relevant information about the product. Here are some of the advantages and disadvantages of swimming pool heat pumps.


  • A pool heat pump is more energy-efficient than other options.
  • It’s a cost-effective solution in the long run. You’re paying less in electricity bills.
  • It is an eco-friendly choice because there is no carbon emission compared to the gas pumps.
  • It’s easy to use and to control the settings.
  • There’s not much noise.


  • Higher upfront costs.
  • It takes some time to heat the water.
  • It might not be the most effective solution in low temperatures.
  • A heat pump requires access to an electrical connection.

How to Make Sure Your Pool Is Always Ready to Use?

Heating the water in an indoor pool versus an outdoor pool is a very different challenge. It is obvious that outdoor tanks are much more exposed to losing heat and evaporation of water; therefore, ensuring the most optimal temperature of the water is this much more critical and (unfortunately) expensive. 

Choosing the right swimming pool heat pump is the first and crucial step in ensuring that you will enjoy using your pool as well as the costs of its upkeep won’t burden you. But there are some other steps you may wish to take in order to maintain your pool in the best condition and lower your costs.

Install a Pool Cover

A great way to ensure the water doesn’t evaporate so quickly is to use a cover when the pool is not used. Of course, the cover protects the water in the pool from dirt, but the other significant benefit of using it is the fact that you’re lessening the evaporation, which means you won’t have to worry about refilling your pool with water as often.

Additionally, you’re lowering the load on your heater pump, which also helps with reducing the costs of operating.

Keep the Pump Uncovered

The heat pump might not be the most aesthetically pleasing view in your backyard, but it is crucial for its proper functioning to keep it uncovered in the open air. Blocking the intake or the outlet of a pump can result in a situation when the device has little warm air to draw. 

Less hot air means that the pump uses more energy to heat the pool. Keeping the pump in the closed space may also lead to an accumulation of cold air from the outlet that, with nowhere else to go, will eventually be drawn back into the pump. This is a situation you should avoid.

Do Regular Maintenance Checkups

Maintaining the pool in the best condition, which includes checking for any leakages and repairing them, will lower your costs. With leaks, you will have to refill the water regularly. It means your swimming pool heat pump will have to run at a higher capacity, so doing regular checkups is a great benefit to you.


Pool (see also ‘The Best Pool Thermometer‘) heat pumps are an excellent choice for those who are looking for something energy efficient and solid. The heat pumps transfer the heat from the air to the swimming pool water. Thanks to this solution, the water can be heated with less cost for your wallet and the environment. 

To find more information about the water heaters and how to resolve any issues regarding these systems, check out our other articles!

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