Using electric heating and a heat pump with your hot tub

Short answer: let the electric element or heat pump keep the water at temperature rather than repeatedly heating it from cold. Regular users set the thermostat to bathing temperature and leave it there; weekend users keep it at around 30 °C on weekdays and raise the setpoint a few hours before use. Always keep the cover on when not in use, so the heating only has to make up for the small amount of heat loss. Below you'll find the settings, hybrid use with a wood-fired heater, and winter operation.

First use

1. Fill the tub to the prescribed level before switching on the heating. An element left dry will burn out; never switch on the heating while filling or draining.
2. Check that the power circuit with residual current device has been installed and switched on by a certified installer.
3. Set the target temperature (typically 37 to 38 °C) and put the cover on.
4. For the very first heat-up from cold mains water, allow for the full heating time: around 16 hours with 3 kW, or around 5 hours with 6 kW or a 7.5 kW heat pump. The full calculation method is in hot tub heating time.

The setpoint strategy

Heating water always costs the same amount of energy (litres x degrees / 860 = kWh); the savings come from retaining heat. Here is how to translate that into settings:

• Daily or several times a week: keep the thermostat fixed at bathing temperature. The tub is always ready, and the element only has to make up the loss.
• Weekend use: around 30 °C on weekdays, raised to 38 °C on Friday afternoon. Going from 30 to 38 takes a few hours; from cold to 38 takes half a day or more.
• Longer absences: turn the heating off. If there is a risk of frost, drain the tub, pipework and equipment completely; see winterising a hot tub.

Two golden rules for every strategy: put the cover on immediately after each use, and keep the tub out of the full wind or shield it. An insulated cover is the cheapest energy saving there is.

Hybrid: wood-fired heater plus element

If your tub has both a wood-fired heater and an electric element, use them in this division of roles:

1. Fire with wood to heat to bathing temperature in around 2.5 to 3.5 hours; this is much faster than electric heating.
2. Then switch on the element at 37 to 38 °C: it holds the temperature for as long as you want.
3. A weekend with multiple sessions then only needs one firing; the element does the rest under the cover.

The complete firing plan is in wood-fired heater use and maintenance.

Using the heat pump properly

A heat pump draws heat from the outside air and, as a result, delivers several times more heat into the water per kilowatt-hour of electricity used. For the best results:

• Give the unit clear space: air must be able to flow freely all around it. Do not build the heat pump into a closed cabinet or tight against a wall.
• Let it do its job: the system automatically reduces its output when little heat is needed. Keeping the water constantly at temperature is exactly what a heat pump is good at.
• Keep it clean: remove leaves, snow and dirt from the grille, especially in autumn and winter.
• Winter: the heat pump keeps working at low temperatures, though the same amount of heat costs slightly more electricity. If you're not using the tub during a frost period, drain it rather than letting the pump run for nothing.

Common mistakes

• Element on while filling or draining: dry running damages the element. Water first, then heating.
• Letting it cool fully every time: heating from cold is the most expensive action; holding the temperature or parking it at 30 °C is cheaper and faster.
• Heating without the cover on: the water surface is the biggest source of heat loss; the heating then runs endlessly.
• Boxing the heat pump in: without free airflow, efficiency collapses.
• Ignoring frost during downtime: frozen pipework and equipment is the most expensive winter mistake.