8: Hot tub heaters gas vs electric?
Most hot tubs are supplied with an integral electric heater, usually around 3 kW output, depending on the water capacity. However, more recently, there has been a growing trend to use gas heating via an external boiler as this is faster at heating up the water compared to electric. This means when you are not using the hot tub, you can keep it at a lower temperature, or even switch the heating off completely, because it won’t take long to bring it up to the temperature when you are ready to use it.
The main reason is the length of time required to heat a hot tub with an electric heater – typically up to 24 hours, using cold water. To speed things up, some owners ‘pre-fill’ their tub with hot water from a boiler, but even this can require a further 6 to 10 hours of heating to achieve the required 38-40 °C temperature.
Whilst many domestic users were prepared to put up with the inconvenience, commercial users such as holiday parks, could not!
The demand for hot tubs when booking holiday accommodation has risen dramatically and is now the second most requested guest facility. To meet this demand, holiday venues had to find a faster way of heating them, due to guest changeover periods. Typically, there is only around 4-5 hours available to drain, clean, re-fill and heat up a hot tub before new guests arrive.
The solution was relatively simple – use an external heat source such as a gas boiler and simply bypass the hot tub’s electric heater. To enable this, a heat exchanger is required to transfer heat from the boiler water to the hot tub water. It’s exactly the same principle used for most swimming pools, but just on a smaller scale.
Bowman developed an ultra-compact heat exchanger that could be installed in the hot tub’s pipework and the result was hot tubs heated in 3-4 hours using cold water, or in around 1 hour using pre-heated water.
There was also another benefit. Heating hot tubs with electricity can be very expensive. By switching to gas boiler heating, many users reported a significant reduction in the energy costs – some as much as £500.00 per hot tub!