Electric pool heater buying guide

In essence, an electric pool heater is no more than a heat-producing electrical resistor along which water flows. Cold water enters at point A; warm water emerges at point B! Complete with a thermostat, the heater turns off automatically once the water reaches a pre-programmed target temperature. In case it still hasn't sunk in, an electric pool heater heats the water in your swimming pool!

Electric pool heaters are installed in the swimming pool equipment enclosure and are incorporated into the filter network. The heated water should be channelled as directly as possible into the pool to avoid heat loss. The heater is positioned between the filter and pump on one side, and the return inlets on the other. Bear in mind, however, that it must come upstream of any water treatment processes such as electrolysis or ionizers. However, the heater should be placed before treatment systems such as electrolysis or ionisers.

If you have the space to open your pool water circuit to include a heater, then yes, any type of pool is compatible. Even so, on larger installations such as inground pools, it's advisable to leave a by-pass so that you can divert all or part of the flow in the event of a heater failure.

Having an electric heater means having a grid connection... so be careful, you might need to include a 30mA circuit breaker!

As you can imagine, while all electric pool heaters look similar and serve the same purpose, they do vary on certain points!

• Material: the body can be made of a composite material, plastic, aluminium, steel or stainless steel. The immersion heater, or the resistor which actually heats the water, can be made of stainless steel or titanium.

• Power rating: this dictates the speed at which your pool temperature rises. Most models are between 3 and 18 kW, but can be up to 45 kW or occasionally even 120 kW.

• Shape: you can get L-shaped and straight heaters.

• Number of resistors: one or two.

• Dimensions: these vary according to the appliance's shape and power rating.

• Thermostat: this is used to set the desired temperature. It can be digital (LCD touchscreen) or analogue (push-button).

• Type of fittings: some models attach to a wall or vertical stand while others are laid horizontally.

• Minimum operating flow: this must be compatible with your pool pump.

• Power supply: single-phase or three-phase depending on your setup.

Consider the use of your pool. If it's primarily for swimming, it may not be necessary to raise it to 27°C. Don't forget that the hotter the water, the greater the algae growth if left unchecked.

The required power rating can be determined by estimating the maximum time you would like the pool to reach the desired temperature.

This power in kW can be estimated by the following formula:

• [(Pool volume x δT) x 1.4] / t , where t is the maximum acceptable heating time in hours and δT the desired rise in temperature.

Here's an example: take a 50m3 pool in a second home. Pool heating starts on Friday evening. It's early summer and the pool has been covered during the week. The water is at 20°C. You want to bathe the following morning in water at 27°C, so the desired rise is 7° in 12 hours maximum. Using the formula that gives us: 50 x 7 x 1.4 / 12 = ~45, so you need a heater rated at 45 kW or more. It couldn't be simpler!...

Top tip: make sure your grid connection can provide a high enough current to power the heater at maximum output!

Simply follow the existing layout of your pool equipment room and the space available. You can choose between vertical and horizontal fittings and an L-shaped or straight shape. The choice is yours!

Top tip: water flow in an electric heater is one-way. Make sure you have access to the thermostat in the chosen layout. In any case, most pool heaters can be reversed fairly easily. It should also be installed low down and equipped with siphon inlets and outlets so that the heating element is constantly immersed in water.

The most appropriate material depends on your planned use.

If you're expecting sustained use throughout the season, choose a metal body - preferably stainless steel. Similarly, choose a highly durable material if your electric pool heater will be exposed to potential damage in the equipment room.

If you just want to occasionally heat an above ground pool, a plastic body will be fine.

If your pool uses salt as a disinfectant you'll probably want to choose titanium for your immersion heater (although some stainless steel elements are now sold as salt-compatible).

As for the number of resistors, having two allows you to limit power consumption once the water has reached its set temperature.

Read the instructions carefully before installation, and combine your electric pool heater with using a pool cover, otherwise watch out for the electricity bill! The smallest electric pool heaters have a power of 3 kW, and quickly reach 9 or 12 kW. For this reason, it is a good idea to fit the control panel with a timer to program heating the water during off-peak hours.

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