Heat Pumps for Swimming Pools

Heat pumps can be a great option for heating homes and have been used for a long time to provide efficient heat to swimming pools too.

However, the type of heat pump you’ll need to heat the water in your pool will depend on several factors like whether your pool is used all year round and whether it is an indoor pool an outdoor pool and how the pool is made.

The type of heat pump you’ll be able to get to heat the water in your swimming pool will also depend on the space you have available around your pool.

Here are the different options you can consider when determining how to heat your swimming pool and which scenarios might best suit you based on the type of pool you have.

What can you use to heat a swimming pool?

Heating the water in your swimming pool isn’t very much different to heating hot water for your home or providing hot water to radiators to heat the rooms in your home.

So, for this reason, methods of heating swimming pool water are often similar too.

Conventional gas or oil fired boilers are both an option for providing heat to your pool but with the cost of fossil based fuels continuing to soar, low carbon options can often provide a good, economical solution for long term efficient heating.

For this reason, both ground source heat pumps and air source heat pumps can be considered as heating options for your swimming pool.

How to choose a heat pump for a swimming pool

There are pros and cons to using air source heat pumps and ground source heat pumps for pool heating and the type of heat pump you choose to providing the heating will depend on things like;

  • whether your swimming pool is “outdoor” or “indoor” i.e. uncovered and exposed to the elements or covered within a purpose built conservatory or building
  • whether your pool is used all year or if it is only used in the summer months
  • insulation available in and around your swimming pool
  • the temperature of the water you prefer for swimming

Choosing the best heat pump for your swimming pool will be much simpler when you have an understanding of each of the above considerations.

Indoor vs outdoor swimming pools

Best for Outdoor Pools Used Only In Summer: Air Source Heat Pumps

Outdoor pools are often only used in the summer, so air source heat pumps can be the best option.

Heat extraction from warm air is more efficient from warm summer air than from ground, so air source heat pumps are recommended for outdoor pools if you pool is only used in the summer and therefore, only requires heating during the summer months.

Air source heat pumps can be switched on and off easily and programmed to operate between certain times of the year to provide heat when you’re swimming most often.

However, if you’re intending to use your pool all year round, even during cooler winter months, then an air source heat pump may not be the best option because air source heat pumps need to work considerably harder when air temperatures are cooler to extract the necessary heat from the air.

This can mean, particularly if air temperatures drop low in the winter, you’ll be faced with a large electricity bill for the increased effort and inefficiency that the air source heat pump has encountered to keep your pool at a consistent temperature all winter.

You could work around this by only heating your pool between 24 and 72 hours before you want to use it through the winter, for example, setting the heat pump to begin heating pool water on Wednesday afternoon in advance of your Saturday morning swim to give the water adequate time to heat up.

Best for Outdoor Pools Used All Year Round: Ground Source Heat Pumps (Space Dependent)

Alternatively, provided you have sufficient outdoor space for a ground source heat pump, alongside it’s loop array system or borehole heat extraction network, you could consider a ground source heat pump.

Unlike an air source heat pump, air temperatures won’t impact the efficiency of heat extraction from below ground and temperatures underground vary to a much lower degree over the change of the seasons than air temperatures do.

Best for Outdoor Pools Used All Year Round Without Additional Outdoor Space: Hybrid Air Source Heat Pump & Boiler System

If you’re limited in terms of additional outdoor space around your swimming pool, making the installation of loop arrays or boreholes impossible, you could consider a hybrid system where an air source heat pump is used to provide heat to your pool in the summer months, with a boiler built in to provide heat for the cold winter months.

Arguably less efficient than an air source system alone, a hybrid system could offer the best way to achieve swimmable temperatures even in the coldest winter months when an air source heat pump might struggle to provide heat efficiently and quickly.

If you prefer warmer water when you swim and would be impacted by a drop in temperature of even 1 or 2 degrees, then a hybrid system might provide the best option for all year round swimming.

Indoor pools will likely require heat all year round, so can benefit from ground source because in the winter months, the temperature of the ground is warmer than the air temperature, so heat transfer can be made more efficient.

Best for Indoor Pools: Ground Source Heat Pumps

Unlike outdoor pools, which can be very seasonal in their usage, indoor pools can often be enjoyed all year round.

For this reason, the demand for efficient, cost effective year round heat is likely higher. Indoor pools also tend to benefit form vastly improved insulation when compared to equivalent outdoor swimming pools, so heat pumps are very often a viable solution for all types of indoor pools.

Provided outdoor space is sufficient to install either a loop array network or boreholes to extract heat from the ground, then a ground source heat pump is likely your best option.

This is because, ground source heat pumps can:

  • easily provide adequate heating to keep your swimming pool water at a consistent temperature
  • you’ll get affordable, year round heat for your pool because of the consistency ground source heat pumps offer
  • ground temperatures stay relatively consistent through summer and winter months, meaning you won’t see a surge in your electricity bills even as air temperatures drop during the winter
  • you’ll pay very little in the way of maintenance fees and upkeep of your heat pump each year
  • HVAC systems can also assist with humidity control of your swimming pool, helping to keep mould, mildew and rust of your pool house to a minimum.

Also, improved insulation can help cut the need for additional heating and help maintain your ideal swimming temperatures for longer helping to keep your heating bills to a minimum.

Air Source Heat Pump vs Ground Source Heat Pump for Swimming Pool: Pros & Cons

Here are the pros and cons of air source heat pumps vs ground source heat pumps, at a glance, for heating swimming pools.

Indoor & Outdoor Pools – Benefits

BenefitsGround Source Heat PumpAir Source Heat Pump
Cheaper bills than an equivalent gas or oil boiler
Affordable year round heating❌ (climate dependent)
Low carbon heating option
Easy to install
Can be installed almost anywhere

Indoor & Outdoor Pools – Drawbacks

DrawbacksGround Source Heat PumpAir Source Heat Pump
Can simultaneously heat your home Unlikely to offer adequate heat outputs for bothUnlikely to offer adequate heat outputs for both
Will be more inefficient in cooler winter monthsSteady, stable efficiencyEfficiency varies
Doesn’t require drilling or excavation work to installRequiredNot Required
Can be installed in areas with very little outdoor spaceSpace NeededLess Space Needed

Insulation Priorities

One of the best ways to improve the efficiency of any type of heating for your swimming pool is through the implementation of insulation methods to help keep water temperatures steady.

Much like in your home, adequate insulation can reduce the need for additional heat and help keep energy costs low.

So before making the change to a heat pump to provide heat to your swimming pool, think about introducing the following insulation types to your pool.

  • Swimming pool bubble wrap insulation – suitable for both the sides of your pool and to act as a cover for the pool when not in use, this solution is easy to install and can help you quickly insulate your pool. Just measure the outer walls of your pool and attach the wrap to the edges of your pool to help keep heat in. This type of insulation material is widely available from Amazon.
  • Rigid pool insulation board – similar to the pliable wraps, swimming pool insulation board can provide a solid insulation around the concrete base and concrete external walls of your pool. Fitted during construction of your pool, these options are perfect for an inbuilt, permanent way of keeping heat in the water in your pool and preventing it escaping quickly into the floor or out through the walls of the pool.
  • Insulated floating pool covers – popular for their ease of installation are the floating pool covers which help to keep light debris out of your pool and also act as a layer of insulation for your pool. These covers can be similar to the pool wall insulation, appearing similar in nature to bubble wrap which floats across the surface of your pool, or can be made from a lightweight durable foam which floats across the top of the surface of your pool to help keep heat in. The foam options are available in different colours and can be up to 12mm thick helping to keep as much heat in as possible.

Insulating your pool room, if you have an indoor pool, can be a complex task because the elevated humidity of pool rooms can leave them prone to high levels of mould, mildew and decay of joists and structures used in the walls and roof of your pool room.

You’ll be best off speaking to a specialist to help ensure your room is adequately insulated, without trapping additional humidity which could lead to issues later.

How does a heat pump work for a swimming pool?

Heat pumps work to provide heat for swimming pools in exactly the same way that they would for a heat pump providing heat for your home.

Air source heat pumps work by taking heat from air outside your property and extracting the heat, usually via a condenser, the heat is then pushed into water which is pushed around pipes in your home to generate heat.

Ground source heat pumps work in the same way, however they extract heat from an underground network installed around your property which absorbs heat into a pressurised network which then can be used to provide heat to your pool through a hot water tank.

In the case of a swimming pool, for both ground source and air source heat pumps, the heat energy would usually heat water in a separate hot water tank, which would then heat the chlorinated water in your swimming pool, because chlorine in water can be corrosive to heat exchangers and pipes found in heat pumps.

You will need to generate a considerable amount of heat to provide enough to keep your swimming pool at a temperature for swimming, so you will need to make sure your heat pump is;

  • a separate system to the heat pump which provides heat to your home and property
  • able to provide the right water temperature to keep your pool at temperatures between 26°C and 30°C.

Can you add a heat pump to an existing pool?

You will generally find that any existing swimming pool can have a heat pump installed to provide heat to the water.

There are considerations you’ll need to make before you commit to installing a pool, these include:

  • whether the pool is inside or outside
  • whether the pool is in use all year or only in the summer months
  • the size, in gallons or litres of the swimming pool (UK average swimming pool sizes are; 10m X 5m for outdoor pools or 9m X 4.5m for indoor pools, 50,000 litres and 40,500 litres respectively at an average depth of 1m.

Location for an air source heat pump – ensure it has sufficient air flow all around it for the best performance

Electricity hook up – safe and certified installation recommended

Pipework – correctly installed to deliver heat efficiently to the pool from the exchanger etc. Factor in flow rate etc for this.

For ground source heat pumps, you need to;

Ensure there’s sufficient outdoor space for the loop array network to be installed, if not consider boreholes to provide the access to the stored underground heat you need.

Plumbing and pipework for adequate flow rate

Electrical supply, safe, certified. Can be installed inside the property because access to external air isn’t needed. Ensure the electrical part is away from splashes likely from the pool.

Pair a Heat Pump with Solar Panels

One option to consider, if you’re retrofitting a heat pump to an indoor pool or having a new indoor pool built is the role that solar panels can play in helping to heat your pool.

Especially during summer months, solar panels could reliably heat water to help feed the heat pump system and provide an additional boost to temperatures in your pool.

Networking your solar panels with a ground source or air source heat pump is possible and fairly simple during the installation of your heat pump, so you’ll enjoy the benefit of diversified heat sources for your pool.

Simply, solar panels can heat water directly with sunlight which can feed the hot water tank which will also be fed by your heat pump, this should help keep the temperature of the water in the tank higher so the heat pump won’t have to work so hard to generate all the heat for your pool by itself.

This could help you save money on electricity required to run your heat pump.

You should make sure your heat pump alone is powerful enough to fully heat your pool because solar heat energy is less consistent.

How to calculate heat pump size for swimming pool

To get a heat pump which is the perfect size to adequately heat your swimming pool you need to know;

  • The volume of water your pool will contain
    • calculate volume by multiplying width, length and the average depth of your swimming pool.
  • The surface area of your swimming pool
    • this is a simple calculation of the length multiplied by the width of your pool.
  • Determine your preferred swimming temperature, for most this will be between 26°C and 30°C
  • Calculate the temperature rise required to achieve this level, so if the ambient temperature of unheated chlorinated water is somewhere between 12°C and 17°C you’ll need a temperature rise of between 13°C to 18°C if you want to hit a balmy 30°C.

You can factor in elements like heat loss rate, however this can be a very complex measurement. If you’re building an indoor pool it might make sense to factor this in, alongside humidity and insulation metrics but it isn’t relevant for outdoor pools where heat loss rates will be very high.

How to Calculate Heat Loss Rate

A simplified example of this calculation is included here.

The formula for heat loss rate is:


This formula essentially breaks down as:

  • Q is the heat loss rate (in watts or joules per second)
  • U is the overall heat transfer coefficient (in watts per square meter per degree Celsius, or W/m²°C)
  • A is the surface area of the pool (in square meters, m²)
  • ΔT is the temperature difference between the water and the surrounding air (in degrees Celsius, °C)

So simplified, heat loss rate = universal heat transfer coefficient X Surface Area of the Pool X temperature difference between the pool water and the surrounding air temperature.

Once you have this, you can determine the heat loss rate from your pool and the size of heat pump you’ll need.

So, if your pool is 9.5m X 4.5m, the average typical size for an indoor pool you could calculate:


Q = 64,800
Q=64800 Watts

With a heat loss rate of 200W per metre squared and a temperature difference of 8°C, your watts would be 64,800.

Or you’d need a heat pump capable of outputting 64.8 kWs to heat your pool.

Heat Pump Size Examples for Your Pool

Using the calculations for heat loss rate, we can estimate the size of heat pump you’ll need for your pool fairly easily.

Larger pools don’t always need a large heat pump to heat them effectively, this is because heat transfer rates don’t drastically increase between pool sizes, so you may find a 64.8kW heat pump is all you’ll need. However, we’d recommend consulting with an experienced professional and calculating your heat loss rate effectively before buying a heat pump.

  • a 25,000 gallon pool – typically a heat pump with a heating capacity of 64.8 kW
  • a 26,000 gallon pool – typically a heat pump with a heating capacity of 64.8 kW
  • or a 40,000 gallon pool and above – speak to a professional

You may have to wait longer if you choose a heat pump which is too small for your pool. So it is always best to check what you need.

How to install a heat pump for swimming pool

You’ll need to make sure your heat pump pool heater is correctly installed to get the best out of it.

How to install an air source heat pump for a swimming pool

For Air source heat pumps you’ll need to:

  • choose an appropriate location with plenty of good airflow all around so the heat pump isn’t recycling cooled air into the system
  • ensure there’s adequate space around and above your heat pump for it to expel air
  • check the flow rate; make sure water flows through the system at the right speed to adequately heat but not so slowly that the pump overheats
  • a water pump may be required to help your water flow reach the required pressure
  • Give your heat pump a solid base; as it’ll be outside all year round, make sure it is correctly supported on a solid foundation that’ll support the heat pump through all seasons and weather conditions.
  • Electrical supply; ideally through a dedicated outlet with circuit breakers for the pump itself. If the heat pump is installed near your pool, ensure the electrical cable is far away from your pool. Usually it is best to put cables underground in an armoured cable to keep them safe.
  • Make sure of your plumbing; check pipe sizes because incorrectly sized pipes can affect flow rates and impact heating efficiency. There are usually only two pipes; a “flow” pipe and a “return” pipe so making sure both are correct, clear sealed is essential.

If you’re installing a heat pump to heat your home, don’t get tempted to use the same unit as you are using to heat your pool. This could cause issues with inadequate heat when you most need it.

Make sure you use a heat exchanger because pool water will often include chlorine will can be corrosive to heat pipes if the water is heated directly.

How to install a ground source heat pump for a swimming pool

Installing a ground source heat pump can be fairly simple, similar to having an extra boiler installed in your home. However, som digging will be required to get your array system setup.

Here are the steps to installing a ground source heat pump for your swimming pool.

  • establish where your ground array or boreholes will be dug to provide heat from the ground
  • once dug and installed, install your ground source heat pump and heat exchanger (these can be located indoors or in your pool house)
  • install a hot water tank to store heated water
  • connect the hot water tank to your exchanger with a feed and connect your pool to the heat exchanger
  • pressurise the system so water flows from the pool into the exchanger and back our again. Ensure water flows from the ground to the heat exchanger too
  • Ensure your heat pump is wired up safely to electrical outlets with necessary breakers and safety features

Once installed, you’ll be able to heat your pool water all year round without burning any gas or fossil fuels.

How much does a heat pump for a pool cost?

Heat pumps suitable for swimming pools start from around:

£2,195 for smaller air source heat pumps or around £4,450 for an equivalent ground source heat pump.

Top end prices for pool heat pumps are around for a ground source heat pump £7,365

Choose the model and features you need carefully to get the best heat pump for your requirements.

Humidity Control for Indoor pools

One of the critical solutions to get right for any indoor swimming pool is effective humidity control.

Humid environments can cause decay to the buildings where the pool is located and the escape of precious heat from your pool.

So an important consideration for indoor pools is maintaining controlled humidity levels.

This can be done by testing humidity of your pool area and employing dehumidifiers or refrigeration techniques through your pool area to help reduce humidity in the air and recapture escaping heat energy from evaporated pool water.

Try a humidity test kit from Amazon to find out the humidity of your pool.

Also try a dehumidifier with a continuous hose for your swimming pools to help keep humidity controlled.