How to Heat a Swimming Pool: The Best Ways Explained

garden swimming pool outside home with patio area
(Image credit: Blue Cube Pools/SPATA)

There are a couple of reasons why you might wondering how to heat a swimming pool. Perhaps you are the owner of an existing pool with inadequate or inefficient heating, or maybe you are planning on installing a new home swimming pool in your garden or indoors.

Whatever you reasons for seeking out the best ways to heat a swimming pool, we have you covered. 

Home swimming pools can provide hours of fun and relaxation, yet they are also a pretty sizeable investment and commitment given that, in the UK, the weather is not always helpful when it comes to tempting you outside to take a dip.

Understanding how to heat a swimming pool in an effective and cost-efficient way is vital if you are to get maximum enjoyment out of your new addition, whether that is a garden pool or an indoor pool.

Our heating guide covers the most popular methods so that you can ensure your pool is everything you dreamt it would be. 

Just as there are many various swimming pool types, there is not just one method of heating a swimming pool — there are, in fact, several different ways.

“There are various ways to heat an outdoor or indoor pool, each with its own merits," explains Chris Hayes, Managing Director at SPATA (The Swimming Pool and Allied Trades Association). "Choosing the right type of heating will help to ensure the most suitable energy-efficient system, which can help to save money on the pool running costs.”

The most common methods of heating swimming pools are:

  • Heat pumps (air and ground)
  • Gas or oil boilers
  • Direct resistance heating

In addition, solar heating is now also sometimes specified by those keen to up the eco credentials of their new garden feature. 

Whichever method you end up choosing, there are several steps you can take to ensure your system can work effectively, to keep running costs down and to reduce heat loss in order that your swimming pool ideas are not hampered by excessive heating bills or freezing cold water.

"SPATA recommends that to assist in minimising operating costs, the use of a heat retention cover should ideally be used with whatever heat source you choose, as most of the heat loss from a swimming pool is from surface evaporation," says Chris Hayes. "However, some heat is also lost through the pool shell walls and floor." This is why it's imperative to insulate a new pool shell if starting from scratch. 

"It is also imperative to ensure that heating equipment is only installed by fully qualified and certified/trained professionals," says Chris Hayes.

night shot of outdoor garden swimming pool

Home swimming pools, such as this from Mermaid Swimming Pools, can be a fantastic addition, but the right heating system will ensure efficient and cost-effective operation.  (Image credit: Mermaid Swimming Pools/SPATA)

Can You Use a Heat Pump to Heat a Swimming Pool?

Using heat pumps for swimming pools is a fantastic, low carbon method of warming up the water effectively and efficiently.

There are actually several different types of heat pump that can be used for swimming pool heating, including air source, ground source and those that are specifically designed for pools. 

Swimming pool heat pumps run on electricity, so you could use photovoltaic panels to power them. They are also very efficient — for every 1kWh of electricity used you could expect to get 3-4kWh of heat, and for this reason they tend to have lower running costs than other options.

On the downside, they are slower to heat pool water compared to fossil fuel heaters. "Heat pumps are generally sized to match the average heat loss from a swimming pool, therefore the initial warm up times are likely to be slower than for other forms of heating — warm up periods of less than five days are generally unlikely," explains SPATA.

You will need to ensure the electric supply to your home is sufficient to cover the additional load of the swimming pool heating — and be aware that, if you use an air source heat pump, some can be noisy to run.

"There are air source and ground source versions of heat pumps. Some heat pumps provide heating direct to the pool water, whilst indirect units utilise a heat exchanger," explain the experts at SPATA. 

"The indirect units have the ability to heat other things (like changing room radiators) as part of a multi zone system, but because they would need to run at higher temperatures, they would be less efficient than a purpose-built swimming pool heat pump."

Using a dedicated swimming pool heat pump, as opposed to a standard heat pump, has other benefits too. They have larger heat exchangers that are often made of titanium in order to withstand the chemical content of swimming pool water. These bigger exchangers allow the swimming pool water to flow through much faster as the swimming pool filter pump is running. This high speed water flow results in a much lower temperature rise per cycle and therefore higher efficiency. 

birds eye view of outdoor home swimming pool

The heating system you choose for your new pool needs to be based on a number of factors, including the design and size of your pool, your budget and even the orientation of your garden. This stunning pool is by Centurion Leisure (Image credit: Centurion Leisure/SPATA)

Which Boilers are Suitable for Swimming Pools?

Using a boiler to heat a swimming pool is a very popular method and gas, oil and LPG boilers can all be used.

"They are available as either a purpose built 'direct' type, where swimming pool water passes directly through the boiler, or an 'indirect' type, where a conventional boiler is linked to an additional external heat exchanger," explains SPATA.

Whichever method you opt for, it is important to realise that the section of the heating equipment that will be in contact with the water has to have been designed to withstand swimming pool chemicals as well as the flow rates required. 

"Some boilers, especially the direct type, can be installed outside, but it is generally more common to install boilers in a plant room," say SPATA.

You could consider using the boiler you rely on to heat radiators and your hot water for your house to heat your pool too.

"As an outdoor swimming pool is heated when the load on a house boiler is at a minimum, it is possible to consider using the house boiler to provide swimming pool heating, through a dedicated swimming pool heat exchanger," explains SPATA. 

"The capital cost of such an installation will be determined by the proximity of swimming pool filtration circuits to the house boiler as pipes and electrical control signals will have to be run between the two. It is also important to ensure that the house boiler capacity is reasonably matched to the swimming pool heating requirement."

What is Direct Resistance Heating?

This type of swimming pool heating is the cheapest to install initially, yet has amongst the highest running costs of all the options. 

Electric resistance heaters are small devices that are designed to be installed within a plant room. Despite their high operational costs, they remain popular due to the fact that they are completely silent to run and require very little in the way of maintenance. 

In terms of the initial heat up period, they are comparable to heat pumps.  

"As with other forms of swimming pool heaters, it is important to ensure that the heater is specifically designed for this purpose," explains SPATA. "Due to the relatively high cost of electricity, they would normally be operated on supply tariffs that offer block periods of lower cost electricity. With the high electrical demand from this type of heating, it is essential that an electrical survey is undertaken to ensure that there is sufficient capacity available."

Can Solar Heating be Used For Swimming Pools?

Solar thermal heating can be a brilliant solution for those after a cost-effective and efficient method of heating their pool — however, there are a few points to note.

When using this type of system, heat is collected from a solar collector (such as panels) and transferred to the swimming pool by means of a heat exchanger. There are several different types of system. You could choose a 'mixed system' that combines a solar thermal heating system with a standard swimming pool heater. Or, in some cases, you may be able to have a system where the energy is generated entirely by a solar thermal system.

"A solar thermal heating system that is integrated into a swimming pool can meet up to 80% of your pool’s heating and energy requirements," according to The Renewable Energy Hub

They go on to state: "To gain the most efficiency from a solar thermal system the system must ideally be located within 25 meters of the house with the solar thermal system mounted on the roof, building or by the poolside."

"Standard pool solar collectors require a bank of panels that are normally over 50% of the surface area of the pool, depending on the location," explains SPATA. 

"Ideally, the bank should be optimised according to manufacturer’s instructions and are angled towards the sun. It is possible that the distance between the filter pump and the panels may require a booster pump which may have to be taken into consideration when designing and siting such a system."

What is the Best Way to Heat an Indoor Swimming Pool?

Although indoor swimming pools have certain requirements that outdoor pools don't, all of the aforementioned methods can be used to heat them. 

You need to bear in mind that whichever heating system you choose for your indoor pool, it takes into account the air heating requirements of the space.

"Heating of the swimming pool air will help reduce moisture evaporation from the swimming pool and provide a comfortable atmosphere for occupants of the room," explains SPATA. "Swimming pool room heating should be complemented with a form of moisture control, such as a dehumidification system, or a combined heating and dehumidification air handling system."

This is because a degree of moisture from the swimming pool water is likely to evaporate into the room causing high humidity levels that could, in turn, cause condensation.

indoor home swimming pool

Although many of the same methods of heating an outdoor swimming pool can be used for indoor pools, you will also need to take into account ventilation and dehumidification systems. This beautiful pool, located in an outdoor garden building, is by Origin Leisure (Image credit: Origin Leisure/SPATA)
Natasha Brinsmead

Natasha is Homebuilding & Renovating’s Associate Content Editor and has been a member of the team for over two decades. An experienced journalist and renovation expert, she has written for a number of homes titles. Over the years Natasha has renovated and carried out a side extension to a Victorian terrace. She is currently living in the rural Edwardian cottage she renovated and extended on a largely DIY basis, living on site for the duration of the project. She is now looking for her next project — something which is proving far harder than she thought it would be.