7: How are hot tubs heated?
Most hot tubs are supplied with an integral electric water heater, which are usually around 3 kW output, depending on the capacity of the hot tub. This type of heater will usually increase the water temperature by around 1 – 2 °C per hour, so it can take up to 24 hours to heat a tub using ambient temperature water.
To overcome this problem, some users fill their tub with pre-heated (25 °C) water from an adjacent boiler, but given that hot tubs usually operate at around 38-40 °C, it can still take a further 6 to 10 hours to achieve full temperature, depending on the performance of the electric heater.
This long heat up time has created a high level of dissatisfaction for many owners, who want their hot tubs to be available for use much faster than the standard heating system allows.
Consequently, many hot tub users, especially those in the commercial sector, are switching to a new type of heating system, using an external boiler, linked to a Bowman heat exchanger. The benefits include significantly reduced heat up times – typically 3 – 4 hours using ambient temperature water, or 1 hour using pre-heated water), plus significantly reduced energy costs compared to electric heating.