Air Source Heat Pumps For Swimming Pools

Pool owners in the UK are increasingly turning to heat pumps for water temperature control. Pool owners and managers must take into account water temperature in order to ensure comfort and ease of use. The most reliable and efficient systems are in increasingly high demand, as more and more users consider energy usage and its environmental impact.

There are many pool heaters on the marketplace, some with confusing descriptions and complex features. We will help you to find the perfect swimming pool heat pump for your needs. We have detailed knowledge and experience of installing the UK’s most popular pool heat pumps, as well as expert knowledge of what to do if they go wrong.

The benefit of using an air source heat pump to heat your pool

This is an important question that many people ask. The most common traditional heating systems that are available for swimming pools are either gas (LPG or propane), oil, or electric water heaters. These heaters can be cheaper to buy but quickly lose their appeal when it comes to running costs. An air source or ground heat pump is a more cost effective, greener solution for heating a pool.

Our swimming pool heat pump services

We are equally able to install an ASHP to provide heat to your indoor or outdoor swimming pool, as one to heat your house. Let’s look at the services we provide:

Pool and infrastructure assessment

We will carry out a full survey of your pool, and related electrical and water, connections, to assess suitability for an ASHP.

ASHP size and type recommendation

Based on the survey and your specific requirements, we can calculate the size of heat pump required, and make recommendations for the brand of heat pump that would work best for you.

System design

Development of the schematics and layout for your ideal system, including all connections to your home’s electrical and pipework infrastructure.


Naturally we can install the ASHP for you! This includes formal commissioning of the unit in line with all relevant industry regulations. If necessary we can also recommend and coordinate the other trades that may be required.

Ongoing maintenance and repair

Once your pump is in place it can be kept at optimal efficiency with a yearly service. We can provide one-off servicing, a regular service contract, or repair any ad-hoc issues that might arise.

Contact us now to find out more about the services we provide!

How swimming pool heat-pumps work

Swimming pool ASHPs work in the same way as one that heats your home. They’re basically a fridge in reverse. They don’t generate heat themselves, but remove it from the outside air and transfer it to the pool water.

The 7 step heating cycle

  1. The refrigeration circulation system heats up the environmental refrigerant gases by absorbing and transferring heat energy.
  2. The fan circulates heat through the outer Evaporator Air Coil.
  3. Liquid refrigerant inside the coil absorbs any heat present in the air, transforming it into a Gas.
  4. The Compressor then pumps out the refrigerant. This heat is intensified or concentrated when the warmed gases are compressed.
  5. This hot gas is then pumped into a Heat Exchanger Condenser. It is here that the heat exchange happens.
  6. The heat from the gas is transferred to the pool water.
  7. Refrigerant is returned to liquid state, which is then pumped into the Expansion Valve

Swimming pool heat pump efficiency

Swimming pool ASHPs are an energy efficient. For every unit of electricity they consume they can be expected to produce up to 5.25 units of heat energy

ASHP efficiency measurement uses the Coefficiency of Performance (COP) number. COP averages at 5.25 across the average range of pump types. It represents the ratio of heat output to energy input, a higher COP equates to lower running costs. COP is dependent on a number of factors, i.e water temperature, air temperature and relative humidity.

As an example, at an ambient air and water temperature of 26°C, a pump with a COP of 6 would output 6kW of heat energy to the pool for every 1kW of energy consumed by the heat pump.

Swimming pool ASHP cost effectiveness

Are pool heat pumps worth it? It won’t surprise you to hear that we believe they are; but here’s why:

While pool heat pumps can be more costly than traditional pool heaters to install, this is usually offset by lower annual operating costs. Pool heat pumps are worth looking into if you’re looking to cut heating costs and potentially extend the life of your outdoor swimming pool.

The cost to run a heat pump depends on its size, ambient temperatures and the temperature you want. To heat a pool 10m x 4m to 28 degrees Celsius, in a UK summer, it would cost about £5 per day given average electricity costs at the time of writing (2023). It would cost more during the time you’re heating the pool up for the season as the heater will be running for longer periods. Costs for gas or oil fuelled heaters can easily be triple this.

Once the pool is warm, the heater should only need to be on for a few hours per day to maintain temperature.

How long does it take for a heat pump heat a pool?

This time depends on the size of your swimming pool, the power of your heat pump, and the temperature outside. In our personal experience, a heat pump will increase the temperature of a pool by between 1 and 3 degrees centigrade per day.

The warmer the external temperature, the faster this will go. This is particularly true of overnight temperatures – in early spring it can be warm in the day but drop low enough at night that a lot of heat is lost.

It will also depend on the power and efficiency of the heat pump, as you’d expect. A new model will heat water much faster.

Seasonality in the UK – when is a pool ASHP most effective

In the UK your pool will be best heated between May and September by a standard air source heat pump. We have received reports from customers who have run heat pumps from April to October due to climate change. With the right size of all-season (also known as “extended”) heat pump it can be possible to run a pool year-round.

We can advise on and fit extended models if requested. Please call us if you are interested to heat your pool beyond May through September.

A heat pump’s balance point is where the heating capability and heating demand meet. Below this point, the heat pump will not be able heat your pool to desired temperatures. You can increase the heating capacity of a heat pump by increasing its size. This will allow you either to attain a higher temperature or prolong the season.

There are many variables which can alter the balance point like pool insulation or pipework. Because of this, manufacturer quoted figures are based only on averages. Heat pumps may not be suitable for all applications or setups or achieve the claimed maximum heating temperature.

What is the minimum ambient temperature for a swimming pool ASHP to be effective?

Although heat pumps can be operated at ambient temperatures below 0 degrees Celsius, they will produce minimal heat. The The ideal temperature for a heat pump is to be turned on is when the ambient air temperature reaches 15-20 degrees. Other conditions like wind, shade and physical position will also affect the shutoff temperature.

At temperatures below 8 to 10°C, summer-only heat pumps are not recommended. Extended season heat pumps have a defrost feature that allows them operate in colder air temperatures (normally less than 8°C). All-season heat pumps will work in temperatures down to -10°C and can be used throughout the year.

Heat Pump Sizing

It is important to select the right size of heat pump to effectively heat your pool.

The size of the heat pump needed will depend upon the size of the pool, its thermal properties, wind speed and water velocity. It also depends on whether you are using a heat retention or heat pump. You should use this rule of thumb: Determine the heat loss per hour (in kW) and purchase a heatpump that exceeds this number.

We will calculate the size of heat pump required for your system for you.

Inverter heat pumps

Inverter heat pumps are an evolution in ASHP technology. They are becoming more widely adopted because of their increased energy efficiency.

When compared to inverter heaters, the disadvantage of on/off heatpumps is that they are dependent on the compressor running at constant speed (maximum) with a fixed frequency. The frequency can be adjusted to suit different needs, but usually it is between 50Hz/60Hz. This method requires that the compressor be turned on/off multiple times and run at maximum noise level to maintain the pool temperature.

Inverter heat pumps are capable of operating in a greater frequency range (20Hz to 100Hz). The frequency can be adjusted automatically depending on the ambient temperature or the desired pool temperature.

They are also very energy-efficient. Because the compressor and the fan can run at different speeds, the heat pump can adapt to achieve the desired temperatures faster and more accurately.

When the pool reaches the desired temperature, the heat pumps can reduce their power consumption by between 25% and 50%. This heat pump can produce a COP of 13, meaning the pump can generate 13kW pool heat for every kW it consumes. They only use what energy is necessary, and only when it’s needed.

An inverter heatpump will save you up to half of the energy that you would need with a conventional on/off model and one-tenth of the energy that an equivalent gas or electrical pool heating solution will use.

You can also influence the rate at which your investment returns. For example, if your pool is heated only from May through August, it will take longer for you to see the return on your investment on a traditional ASHP model. However, if your pool is heated all year long, the inverter type will pay back much quicker.

Ask us about the types of inverter heat pump we can install and maintain.

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