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Swimming pool boiler or heater – Gas boilers for swimming pools

swimming pool boiler; gas swimming pool heater; pool heaters; warm water; heater; swim;

A swimming pool boiler is very much like a domestic boiler in that they generate heat by burning gas inside a combustion chamber within the energy-efficient boiler; this heat is then transferred to swimming pool water, via a heat exchanger (which is titanium in our dedicated pool boilers), which is subsequently pumped back into the swimming pool, resulting in a comfortable temperature for swimming and making them a fantastic long-term investment for swimming pool owners.

Some people often refer to swimming pool boilers as swimming pool heaters; they are, in essence, exactly the same thing. They warm the water to your desired temperature, resulting in a comfortable pool water temperature in your swimming pool. Only condensing pool heaters should be used now due to the ErP regulations for swimming pool heating.

In the United Kingdom, gas boiler systems are the most common method of pool heating. They regularly outsell heat pumps due to the speed at which they can warm a pool to ensure you can swim whenever you want and the fact that they are not dependent on air temperature, allowing them to be used all year round, unlike a heat pump heating system.

Our highly efficient condensing technology swimming pool gas boilers have lower running costs than an electric pool heater. Our gas boiler range for swimming pool heating is one of the few in the UK’s condensing pool heaters to be powered by either propane gas ( LPG) or natural gas (mains gas). They are also more cost-effective to purchase than an electric pool heater or heat pumps.

Energy efficiency

A gas swimming pool boiler is highly energy efficient these days, as condensing boiler technology ensures the maximum heat transfer from the boiler’s exhaust gases into the heated water. Our condensing pool heaters, or swimming pool boilers, are up to 106% efficient, as these boilers recover the latent heat from the flue gases via a stainless steel heat exchanger as they heat pools with condensing technology.

Unlike an air source heat pump, our running costs and efficiency are not affected by the external weather temperature, when you use our swimming pool boiler.

With our condensing swimming pool boiler, you can rest assured that you are getting an energy efficient pool boiler, resulting in lower costs to heat your pools, hot tubs, or spas in domestic or commercial situations, especially when compared to an electric pool heater, as an electric heater can be very expensive to heat your pool.

An air source heat pump relies on a high external air temperature to operate efficiently and will have to go into a defrost cycle if the air temperature is too low. When using electric heaters to defrost, an air source heat pump efficiency drops considerably with a lower external air temperature.

These swimming pool gas boilers can also be used as a backup solution or in conjunction with solar heaters or solar panels as an energy source, to top up the water temperature on cloudy days, as solar panels or solar heaters as an energy source aren’t as effective in these conditions.

Swimming pool heaters gas fired

Gas condensing swimming pool boilers utilise the latest cutting-edge technology to deliver effective and quick pool heating. Our gas pool heater range, with an energy efficiency rating of up to 105 percent, may save up to 32 percent on operating running cost when compared to an older non condensing swimming pool boiler.

Our swimming pool gas heaters / pool boilers can be fired by either natural gas or LPG gas (propane gas).So whichever gas you decided to power your gas boiler, we have you covered for both indoor or outdoor pools.

swimming pool heater gas fired from Flexiheat UK:water heater:natural gas:propane gas:stainless steel heat exchanger

Swimming pool heating from Flexiheat UK

So you also wish to change your gas over to from LPG to natural or vice versa , this is easily done with a simple gas conversion kit to suit, which is an easy installation to do by any plumbing company that holds the relevant certificates for working on these gases.

Swimming pool boiler range with inbuilt titanium pool heat exchanger

Swimming pool boilers which are condensing pool heaters gas fired from Flexiheat UK

A floor standing swimming pool boiler range from 34 kW up to 280 kW in single piece boilers, and up to 2,240kW in cascade (8 x 280kW units). These are modulating gas condensing pool heater with a 100% Titanium heat exchanger which heats the swimming pool water directly, so there is no need for an additional plate or tube heat exchanger in the pool heating scheme.

Advantages of our swimming pool boiler with inbuilt titanium pool heat exchanger from Flexiheat UK

Advantages of our swimming pool boiler range with inbuilt titanium pool heat exchanger from Flexiheat UK

Swimming pool boilers gas fired

Another benefit of our boiler range is that we can do an external combi version that will not only heat your swimming pool but also produce domestic hot water for showering, etc. This is another reason we have the best boiler range for a swimming pool. We can warm water, not only for heating the pool via a separate pool heat exchanger but also for the domestic water required after you’ve had a swim, which is an extra versatility that many of our competitors on the market cannot provide.

Our external combination pool boiler (the boiler services both the pool heating and domestic hot water heating system requirements) benefits from being compact in size, thus saving space and installation time in your pool boiler room. This external unit not only saves even more space but also saves on the installation of a flue system, as these units have a forward-facing flue installation configuration that efficiently and neatly fits onto the pool boiler (see pictures below).


external gas pool boiler; external gas pool heater

External gas pool boiler or heater in natural gas or propane from Flexiheat UK

Another benefit of an external gas fired fully weatherproofed pool boiler is that you can service or maintain the boiler without having to have access to the property. The same is applicable for any repairs that may be required to the heating systems.

Safety is also another benefit of an external installation of a swimming pool boiler, as there’s no risk of CO2 poisoning as the swimming pool boiler is situated in the external air environment. Another installation safety feature that an externally mounted gas boiler benefits from is that if there’s a gas leak, the gas is dispersed into the free external air.

If you require a new boiler or pool heater, then our best advice is: if you want a boiler / pool heater to heat your pool along with a requirement for domestic hot water services, then you should consider one of our reliable combination swimming pool boilers.

Because of the speed at which they can heat a pool and the fact that they are not dependent on air temperature, gas pool heaters regularly outsell heat pumps, allowing them to be used all year.

Swimming pools boiler/ heater sizing

Variables such as having a solar cover, temperature, and how frequently you use the pool can all have an impact on the effectiveness of your boiler, and need to be accounted for to ensure your never left with cold water when you want to have your daily swim.

The evaporation of water from the surface accounts for the majority of heat loss from a swimming pool surface and a little through swimming pool liners. Thus this following table is based with a swimming pool covers ,which covers swimming pool , to avoid any heat losses caused by wind conditions and evaporation.

This pool boiler / heater size guide is for outdoor swimming pools in the South of UK, from late April until early October ( basically summer swimming) . For northern UK swimming pools, you may need to increase the gas heater size by 30% to 50%, depending on the swimming pool’s exposure.

To get the most out of your swimming pool heating system it is highly recommended that you use the 60 Degrees C temperature on the below pool sizing chart, as when the boiler heating water flows out at 60C and return water comes back at 40C, the boiler will always be in the maximum energy efficient condensing state, thus reducing the swimming pool heating systems running cost.

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Swimming pool heat exchanger data for gas fired boilers from Flexiheat UK for pool heating

To be fair you can never over-size one of our gas boilers for a swimming pool , as the are full modulating and will adapt the output to the pool heating requirements, the larger the gas boilers are the quicker they’ll warm the pool water from cold water- its as simple as that .Our top tips or advice as a company is – There is very little cost difference, from one of our 25 kW gas boiler to our 30kW boilers for example – so go for the larger heater or boiler swimming pool / pool boiler.

Please remember all gas boilers should only be fitted (installation process) by a gas safe registered engineer and should be serviced regularly i.e. serviced annually. Remember gas regulations and gas safety is paramount when it comes to a gas boiler or gas heaters that heat your pool -regular servicing ( annual servicing) is vital.

In the same manner the annual service must be performed by a gas safe qualified engineer.

Gas boiler range

Our reliable and efficient swimming pool gas boiler range for pools – are available in LPG (also referred to as propane), which sometimes leads to customers calling them a propane pool heater or in natural gas (mains gas) versions. Either fuel, can be referred to as a gas swimming pool heater.

Our gas pool heaters are fully modulating, which means they provide a precise and clean burn with a correct air/fuel combination every time they operate, ensuring a boiler is kept in top condition, and running efficiently. When run at 60/40C flow and returns, you’re operating at the best energy efficient temperatures, which means that the boilers are 105% energy efficient, reducing your heating costs.

Of course, you can operate the pool heaters at 80/60C, which will result in a faster heater up time, but will consume more energy as a result. It is your choice as the best option for you to heat your pool depending on your requirements.

We do a 24kW, 28kW,34 kW, 50kW, 60kW, 75kW, 100kW and 115 kW gas fired external swimming pool heater in single boiler units, or we can cascade the swimming pool heaters up to 960 kW, so we can heat your pool whatever the size is.



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Singular Boilers – 24kW to 115kW Output


You have two options for heating your pool with gas.

A dedicated floor-mounted unit with an internal heat exchanger that heats the pool water.The advantage of this system is that it is one compact unit with everything built into it, and there are fewer elements to the system.

Downside: Cleaning the heat exchanger will require some disassembling of the boiler, which really should be done by a suitably qualified person (such as a gas safe registered engineer).


An externally mounted unit, used in conjunction with a separate pool heat exchanger.

Advantages of this set-up: You don’t have to touch the boiler if you want to clean out the pool heat exchanger.

The downside is that there are more components in your heating system.

Which is best for service and repair

Easy, just separate the gas boiler , and the heat exchanger for the pool water – You have the same system or services as the older technology – just in two separate components –

There will be fewer problems because the pool water does not enter the energy-efficient boiler. The pool heating is done via dedicated specialist heat exchanger – which can be corrosion resistant titanium or similar construction.

What’s the benefits?

There are many –

Mounting options –

You can mount the heat exchanger in either a horizontal or vertical orientation, to suit you site requirements from your swimming pool pumps

Swimming pool heat exchanger mounting options Flexiheat UK

System diagram showing pool pump and swimming pool filters for the pool heaters


Service / Maintenance

Service / maintenance of the pools heat exchanger – it’s incredibly easy on the day  – just remove the end caps, and then you can pull out the elements for inspection / cleaning.

Swimming pool heat exchanger instal picture for use with gas swimming pool heating Flexiheat UK;heat pump;british thermal units

Heat exchanger for pool heating coupled up to a gas fired heater / boiler

Boiler repair, plumbing or gas safety checks is also easier when the two heaters are separated, unlike the Certikin genie heaters and other brands on the market. Gas safety services checks should be done annually.

swimming pool boiler exchanger for heated water

Easy to access and clean heat exchanger – no disassembling of the boiler (you need to be gas safe registered engineer to do this- as per the gas regulations) – thus regular servicing is easy and uncomplicated.

Oil Fired pool heaters

Domestic fuel oil is burned in a specialised swimming pool oil heater; again, they work in the same way as a domestic boiler in that they have a combustion chamber, where the oil is burned, and that heat transfers into the pool’s water, normally via a central exchanger of either stainless steel or titanium. An oil pool heater is initially expensive to buy, install, and service when compared to a gas-fired swimming pool boiler.

They also have some other disadvantages.

  • Oil is a fossil fuel with higher carbon emissions than gas, so you’re contributing to a larger impact on the environment if you use oil as the heating system fuel.
  • Fuel cost to heat your pool water: oil boilers have relatively high running costs; only second to electricity for heating pools, a gas boiler is the most recommended, most convenient, and cheapest at present. Your daily swim will cost less with a gas-heated swimming pool boiler.

Contact us 

If your after a new swimming pool boiler, should you require any advice or more information on our reliable gas fired swimming pool heaters or swimming pool gas boilers to suit any size swimming pool from domestic to commercial, that will give you many years of effective trouble free operation, then give our friendly sales team a call on 01202 822221 or use our contact form above on the website.