How Do Pool Heat Pumps Work?

Having a swimming pool at home allows you and your family to take a refreshing dip whenever you feel like it. Moreover, it enables you to have pool parties and poolside gatherings. Although swimming pools are usually used in the summer, you can also swim in slightly chilly weather, but you will need a pool heat pump to heat the water.

A pool heat pump warms up the water inside a swimming pool. The heat pump shifts the heat from one corner of the pool to the other. However, they are incapable of generating heat.

During this process, the water goes through the filtration system and the heat pump. This way, the water is heated and cleaned at the same time.

Let’s see how the pool heat pump works to regulate the water temperature inside your swimming pool.

How Do Pool Heat Pumps Work

The Function of a Pool Heat Pump

The pool heat pump consumes electricity but doesn’t generate heat. However, heat is absorbed from the atmosphere via the heat pump’s fan. The fan sucks in hot air, which is then spread across an external evaporator. The liquid refrigerant inside the evaporator coil takes in the heat and converts it into gas.

The gas, which is now hot, is pumped into the compressor from the coil, adding heat and producing a high-temperature gas. This then goes via the condenser of the heat exchanger.

While circulating the water from the pool, the water passes it through the filter and the water heater of the heat pump. Since the liquid refrigerant and pool water reach the heat exchanger together, the hot gas heats the water.

The water temperature increases by 3 to 6 degrees after contact with the hot gas and this water is pumped back to the pool. Finally, the gas is turned into a liquid and sent again into the vaporizer, restarting the entire process.

The heater works efficiently until the outdoor temperature stays above 45 to 50°F. If the outdoor temperature is low, it will require more energy to heat the water. However, swimming pools are mainly used during summers, so high energy consumption is not a big problem.

The ability of a device to heat the water flowing through it depends partly on the temperature of the ambient air entering the heat pump. The warmer the outdoor air, the warmer the inside of the device, and the warmer your swimming pool.

Once the temperature starts to drop, the heat pump can no longer heat the water. The ambient temperature must be approximately 10°C (50°F) or higher for the device to function correctly.

In addition, the more heat the heat pump extracts, the more humid the air. This makes the heat pump an ideal choice for swimming pool heating in hot conditions.

The Water Heating Process

The compressor is powered by electricity, and it sucks in freon, which evaporates from the liquid-filled evaporator tube. The temperature difference causes a cooling effect, much like how sweat affects the human body once it evaporates.

This gas is compressed, and its temperature exceeds 200°F (93°C). As a result, the gas is heated by five thermal units. The pressurized gas flows through the condenser coil.

The coldest pool water at 26°C (80°F) collects five units of heat from Freon and cools it back to the hot liquid. When the pressure drops, it expands rapidly and becomes a very cold liquid—the liquid returns to the evaporator, and the cycle repeats.

Heat pumps for swimming pools are specially designed for recreational pools. Most appliances in your house contain heat pumps, such as the AC, dehumidifier, fridge, or freezer. These devices use electricity and a sealed refrigerant compression system to transfer heat from one location to another.

Different manufacturers use different methods to determine the performance levels and efficiency of heat pumps. This is why the values can vary from equipment to equipment.

As there is no standard test to measure the energy efficiency of a pool’s heating system, the best way is to test different heating systems before making the final purchase.

How to Determine the Size of the Pool Heat Pump

A trained pool professional can perform a proper size analysis for your specific pool. Determining the dimensions of a pool heating system with a heat pump depends on many factors. These include:

  • Cool night temperatures
  • Humidity
  • Wind load
  • The surface area of the pool
  • Average air temperature

This is why swimming pools located in areas with cooler nights, lower humidity, and higher surface area surface winds are more difficult to heat.

Heat pump pool heaters are rated for BTU power and horsepower (HP). Standards include:

  • 3.5HP/75,000 BTUs
  • 5HP/100,000 BTUs
  • 6HP/125,000 BTUs

To determine the approximate size of the heater for an outdoor pool, proceed as follows:

  • Determine your desired pool temperature
  • Determine the average temperature for the coldest month of pool use
  • Subtract the average temperature for the coldest month from the desired pool temperature. This will give you the necessary temperature rise
  • Calculate the area of the pool in square meters


When getting a heat pump for your swimming pool, make sure to consider the above factors. Then, choose one that suits your requirements, such as desired temperature, the lowest average outdoor temperature, and other factors.

Once you have your heat pump, hire an experienced and licensed professional to install it for you.

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