Heat Pumps for Swimming Pools: The Low Carbon Route to Warm Water

heat pumps for swimming pools have been used to heat this pool
(Image credit: Simon Maxwell)

Did you know you can use heat pumps for swimming pools? A swimming pool can potentially be heated by any heating appliance, but a heat pump can be a very efficient and low carbon method of heating the pool water.

While standard heat pumps can be used for swimming pools, there's also an option of efficient, less expensive heat pumps specifically designed for pools that you may also be able to take advantage of. 

We explore the key information you need to know when looking at heat pumps as a heat source for your swimming pool. 

Why Choose a Heat Pump for a Swimming Pool?

A swimming pool can be heated by a domestic hot water heat pump via a suitably sized heat exchanger or alternatively a dedicated swimming pool heat pump can be used. 

A domestic hot water heat pump will usually have a slower flow of water through its heat exchanger and the resultant temperature rise in that water will be higher that a dedicated swimming pool heat pump which will have its own heat exchanger (usually made of titanium to be resilient to the pool water chemicals) that is plumbed in series with the pool pump and filter system. 

The water flows very fast through the heat exchanger and the temperature rise is very low, sometimes under 1°C. This low temperature difference allows the heat pump to be very efficient, often achieving efficiencies of over 500%. 

What Type of Heat Pump Should I Use for a Swimming Pool?

All types of heat pumps can potentially be used to heat a swimming pool but the choice of which one is ideal for your project will be determined by your specific requirements. An indoor pool will be used all year round so therefore the heat pump needs to be capable of operating in winter conditions as well as achieving the required water temperature at those times. 

The swimming pool will have a fairly high energy requirement and as such a ground source heat pump will need a ground loop that is sized for that load. If the ground source heat pump is also providing the heat to the home and sanitary hot water then the maximum heat load of the home, hot water load and the swimming pool load will need to be calculated and the unit sized and ground collector (either horizontal loops or borehole loops) to cope with the highest load in winter but also be capable of covering the smallest loads in summer without going into short start-stop cycles. 

Many European heat pumps have a limited number of starts per hour and if that is done in the first 10 minutes then the unit will not turn on again for an hour.

Air source heat pump powering timber clad renovation with swimming pool

Heated by an air source heat pump, this 7.5m x 3.6m pool installed in a home on the Isle of Wight also has a hydrojet so that it can be used efficiently for exercise.  (Image credit: Alistair Nicholls)

How Do Heat Pumps for Swimming Pools Work? 

A standard medium or high temperature heat pump can be used to heat a swimming pool if plumbed to an appropriately sized heat exchanger but there are also dedicated swimming pool heat pumps as well. 

A swimming pool air source heat pump is usually a simpler product than heat pumps you would see connected to a home for central heating and hot water. The swimming pool air source heat pump has a larger heat exchanger (usually made of titanium to be resilient to the high chemical content in swimming pool water) that allows the swimming pool water to flow through it a lot faster as the swimming pool filter pump is running. The higher speed of the water flow results in a much lower temperature rise per cycle and therefore higher efficiency. 

Because there is now circulation pump and also low temperature rise and usually a higher ambient air temperature the average efficiency can be over 500%. Therefore, for every 1kWh you use to run the heat pump it will deliver 5kWh of heat to the swimming pool. 

Can I Use a Heat Pump to Heat a Swimming Pool All Year Round?

A dedicated swimming pool heat pump is usually used when the ambient air temperature is high and therefore is not always suitable for all year use. 

Many of them do not have a defrost cycle as they are predominantly used on outdoor swimming pools in warmer climates, so they may not be suitable for use in winter. 

You can however use the more domestic type heat pumps if you have an indoor swimming pool that you intend to use all year round.

How Long Does a Heat Pump Take to Heat a Pool?

An appropriately sized heat pump will usually heat the swimming pool in around 4 to 5 days.

However, you can make a more accurate estimate for a specific swimming pool with this formula:

Seconds = Litres x 4.18 (specific heat capacity of water) x temperature difference / kW

Therefore if you have a 12kW heat pump on an 8m x 4m x 1m (average depth) swimming pool that you want to heat to 25 degrees (lets assume the cold water is 5 degrees) then here is the calculation:

Seconds = 32000 x 4.18 x 20 ÷ 12

This equals 222, 933 seconds, or 62 hours

This does not take into account any heat loss during the heat up time so that needs to be added.

How Efficient are Heat Pumps for Swimming Pools?

A dedicated swimming pool air source heat pump can realistically be around 500% efficient meaning that for every kWh of electricity that it uses it will produce 5kWh of heat. The efficiency of the heat pump is directly proportional to the ambient temperature of the air and the target temperature in the water. The further those two temperatures are apart the lower the efficiency

heat pumps for swimming pools have been used to heat this pool

Joy Cousins chose to install a swimming pool during the renovation of this home. It is heated by a heat pump and has a retractable cover.  (Image credit: Simon Maxwell)

Pros and Cons of Heat Pumps for Swimming Pools

There are some reasons for and against heat pumps as a heat source for your swimming pool. 

On the plus side, heat pumps use electricity so you can use the generation from photovoltaic panels to power the heat pump. 

They're also incredibly efficient, and for every 1kWh of electricity used you can potentially get 5kWh of heat.

However, swimming pools require a lot of energy to heat, so you'll need to ensure the electric supply to the home is sufficient to cover the additional load of the swimming pool heating.

Heat pumps are not as fast as heating pool water in comparison to fossil fuel heaters, and there could be a noise associated with air source heat pumps

Are Heat Pumps for Swimming Pools Worth It?

A swimming pool heat pump can be a very efficient way of heating a swimming pool, especially if you have a source of electric generation on your home such as solar PV panels. 

Given the potentially higher levels of efficiency a heat pump can be the best value for money when compared with other heat sources, especially during the summer months. If you have an indoor swimming pool that you use all year then a seasonal efficiency needs to be calculated and compared against alternative heating fuels.


What Size Heat Pump Do I Need for my Swimming Pool? 

The size and heat loss of the swimming pool will need to be defined and then a suitable heat pump specified to cover the heat loss and also have the capacity to reheat the swimming pool should you allow it to seasonally go cold. 

Many swimming pool circulation pumps will run for around eight hours a day. The heat pump should be able to deliver the required heat to the pool during those hours. If reheat is required then the pool pump is run for longer. An indoor swimming pool will have a lower heat loss than an outdoor pool but with an indoor pool you will also need to allow for heating the air in the pool room and also circulating that air. It is usual to maintain the air temperature at around 3 degrees warmer than the water temperature to mitigate evaporative losses. 

Air circulation is at a lot higher rate than what is required in a domestic home so it is not suitable to use a standard mechanical heat recovery ventilation (MVHR) unit for this. A dedicated swimming pool ventilation unit is required and very often these units can also manage the delivery of heat to the air and the swimming pool water.

an indoor swimming pool in a timber outbuilding

(Image credit: getty images)


How Much Does a Heat Pump for a Swimming Pool Cost?

The dedicated swimming pool heat pump can be a lot less expensive than the air source heat pumps that are typically plumbed to our homes for central heating and hot water preparation. 

(MORE: Air Source Heat Pump Costs Explained)

Dedicated swimming pool heat pumps start at around £1,500, but for a full air handling unit with heat management capabilities you could be looking at upwards of £15,000. 

Do your research and define your needs as costs can escalate quickly.

Running Costs of Using a Heat Pump to Heat a Swimming Pool

The running costs of a swimming pool heat pump will be directly proportional to the heat loss of the water. 

An outdoor swimming pool will usually have a significantly higher heat loss than an indoor swimming pool due to evaporative losses, lack of insulation and expose to cold winds. 

As a very general guide, look at the surface area in square meters and then use around 200W per square metre for an exposed outdoor swimming pool down to around 50W if the swimming pool is in a protected location with a good thermal cover. 

An indoor swimming pool will have less heat loss if the air in the pool room is warmer than the water. This air heat loss should then be included in the running cost for the heating of the swimming pool.


What Does Installation of a Heat Pump for a Swimming Pool Involve?

Installation of a heat pump to heat a swimming pool could be a simple as plumbing the unit in series with the return flow or water from the filer to the swimming pool, but in an existing indoor swimming pool there may also be some substantial building work required to access the pipework and then route it to the heat pump.

Can I Add a Heat Pump to an Existing Swimming Pool?

Yes. This can be a very simple installation if there is space near the swimming pool pump and filter and there is also a robust enough electricity supply. On an existing indoor pool or where space is limited and the pipes are all built into the landscaping then make sure you get a survey and on site quote.

an outdoor infinity swimming pool

(Image credit: Nigel Rigden)

How to Find a Heat Pump Installer for a Swimming Pool

Many swimming pool contractors will already have experience of working with these products so start there. They know the swimming pool products, types of chemicals, heat exchangers, heat loss expectations, reheat times and typical temperature requirements. A domestic heating engineer may not have the experience of working with swimming pools. 

Buying a Heat Pump for a Swimming Pool

Where Can I Buy a Heat Pumps for a Swimming Pool?

The first contact should be your swimming pool contractor. Alternatively speak with the heat pump manufacturers and get the list of approved installers with swimming pool experience.

What’s the Best Heat Pump for a Swimming Pool?

It is fair to say that you get what you pay for. Swimming pool water is corrosive and the components need to be robust enough to cope with the chemicals and the potential exposure to the weather. Also make sure that the heat pump has been correctly sized and specified for your situation. 

Calorex and Heatstar have been manufacturing specialist swimming pool heating systems for many years but there are also now many more products on the market as well as many domestic heat pumps that can be plumbed to a swimming pool via a heat exchanger.

David Hilton

David is a renewables and ventilation installer, with over 35 years experience, and is a long-standing contributor to Homebuilding and Renovating magazine. He is a member of the Gas Safe Register, has a Masters degree in Sustainable Architecture, and is an authority in sustainable building and energy efficiency, with extensive knowledge in building fabrics, heat recovery ventilation, renewables, and also conventional heating systems. He is also a speaker at the Homebuilding & Renovating Show. 

Passionate about healthy, efficient homes, he is director of Heat and Energy Ltd. He works with architects, builders, self builders and renovators, and designs and project manages the installation of ventilation and heating systems to achieve the most energy efficient and cost effective outcome for every home.