Guide written by:
Patrick, Handyman, Bath
A swimming pool kept at a constant 27°C, what a luxury! If your central heating system is located near your machine room and pool, the pool heat exchanger is for you! Simple and economical, it ensures a rapid rise in water temperature. Heating power, water volume... Here's what you need to know!
- Water volume
What exactly is a heat exchanger?
A pool heat exchanger has two water circulation circuits:
- A "primary" circuit, connected to the property's central heating;
- A "secondary circuit", in which the swimming pool water circulates.
These two circuits meet in parallel at the centre of the heat exchanger, and the primary circuit transfers its heat energy to the secondary.
That's all there is to it!...
How does a pool heat exchanger work?
To use a pool heat exchanger, two conditions must be met:
- You must have a domestic boiler;
- This must be installed close to the pool and machine room.
The type of boiler is immaterial. Whether it's a conventional oil or gas boiler or a heat pump, you can use it to power your heat exchanger. You must however ensure that its power level is sufficient.
If you only heat your pool when you're not using the central heating (e.g. in the summer), then your boiler should definitely be powerful enough. However, you'll need to think more carefully if you want to heat your pool while the central heating is in use (for an indoor pool, for instance).
The proximity of the machine room and boiler is crucial, or you risk losing a significant amount of heat. Ideally, they should be located in the same room to optimize energy transfer.
How to size your pool heat exchanger?
The required power of the heat exchanger depends on the size of the pool and the temperature rise time you're aiming for.
In general, the devices are scaled so as to gain 10°C in 2 days.
The table below shows minimum heat exchanger power ratings for different pool sizes. The power of the exchanger conditions the bulk and its consumption but also its cost of purchase.
Minimum heat exchanger power
If you want a more precise estimate for your size of pool, the following formula will give you intermediate values:
Power (in kW) = Volume (in m3) x 1.4 x DeltaT / T
Where T is the desired temperature rise time for your pool and DeltaT is the difference between the initial temperature and desired water temperatures.
So, calculate your required power value, but don't be too thorough. Over-sizing a pool heat exchanger will add to its purchase cost; once the desired temperature is reached, less heating power is required to maintain it. Also think carefully about temperature rise time: a large inground swimming pool doesn't necessarily need to reach the optimum temperature in 2 days, whereas a small above-ground pool for occasional use only will need to be heated quickly.
Important: recommended power values are given for an assumed primary circuit water temperature. In reality, this temperature will vary according to the characteristics of your central heating. A boiler will deliver water at a higher primary temperature than a heat pump - usually 90°C as opposed to 45°C. Also, if you want to connect a heat pump, check that your heat exchanger is compatible with the temperature of your primary network.
What other factors are important when choosing your pool heat exchanger?
Pool heat exchangers require minimal flow.
It's essential to ensure compatibility between your boiler and exchange circulator.
Flow rate must not exceed a certain maximum value, so installation of a bypass is essential.
What are the different types of pool heat exchanger?
There are two main types of swimming pool heat exchanger:
- Tubular heat exchangers - where the water circulates in tubes;
- Plate heat exchangers - where heat exchange is achieved via parallel radiating plates, one of which belongs to the primary circuit and the other to the secondary circuit.
At equivalent power ratings, tubular heat exchangers are generally cheaper and less bulky than plate heat exchangers, although these latter have the advantage of operating at lower primary temperatures, making them more suitable for use with heat pumps.
Final advice on choosing your pool heat exchanger
If you're using electrolysis as a disinfectant method, or have a salt water pool, the heat exchanger tubes or plates must be made of titanium rather than stainless steel.
Swimming pool heat exchangers may come with or without a circulator, so be sure to check if your installation requires the addition of a circulator. This will certainly be the case if you're using your boiler to power the central heating and heat the pool at the same time, it all depends on the type of installation and connection you have.
Not all pool heat exchangers have a thermostat, so choose one that includes this useful feature where possible.
Final advice: Since installing a heat exchanger involves modifying your main central heating system, be especially careful. Always read boiler and heat pump instructions thoroughly.
Learn more about swimming pool equipment...
To find out more about swimming pool equipment, follow our editors' advice and discover their other guides:
Guide written by:
Patrick, Handyman, Bath, 12 guides
Professional maintenance and electronics training. I don’t ask to use my tools on the weekend. The car, the boat, the house with its electric appliances, the garden and its swimming pool, they all remind me that they need my attention. In the absence of an unlimited budget, I try to expand my areas of expertise. There’s nothing I like quite as much as being in the weekend workshop with my buddies. Everyone benefits from his experience which ends up being more-or-less successful, it must be said. But that’s part of the charm of DIY, helping each other and realizing a project in a pleasant way. So, if I can help you, it would be a pleasure.