Is a Heat Pump Worth It for a Hot Tub?
One unit of electricity in, five units of heat out.
That is why a heat pump is worth it if you keep your hot tub hot all year. It takes warmth from the outside air and moves it into the water: about 5.4 kWh of heat for every kWh of electricity on our 7kW heat pump in 15°C air, where the hot tub's own heater gives 1.1
How a heat pump heats your hot tub
It moves heat rather than making it.
A heat pump takes heat from the outside air into a refrigerant, and a compressor raises its temperature so it can pass that heat on.2 In a hot tub heat pump, the hot tub water flows through a titanium heat exchanger inside the unit and comes back warmer.1
The heater built into a hot tub turns electricity straight into heat, so 1 kWh of electricity gives about 1 kWh of heat. The heat pump's extra comes free from the air. How much extra is its COP, the heat out divided by the electricity in.
What one heat-up costs
Take a 1,000 litre hot tub, the size of our Lagoon, and warm it by 10°C. Water needs 4.18 kJ for each kilogram and each degree, so that is about 11.6 kWh of heat.3, 4 At the price cap rate of 26.32p per kWh,5 here is what that heat costs.
Bars drawn to scale. Heat pump figures use our 7kW heat pump's COP at each air temperature, with 26°C water.1 Heat lost through the cover and the cabinet adds to both, so a well fitting cover helps either way.
Still ahead in winter
Cold air, still more heat
A heat pump gives less in cold air, but it stays well ahead of a heater. At -7°C our 7kW heat pump still has a COP of 3.05, so each kWh of electricity becomes about 3 kWh of heat.1
Who gains the most
Hot tubs kept hot all year
Every kWh of heat the heat pump supplies costs a fraction of the same kWh from the heater, so the saving grows with every week the tub stays hot. A swim spa holds about five to ten times as much water as a hot tub, which makes the difference bigger still.
Our heat pumps
See all our air source heat pumps, or start with these two.
Outdoor Living 7kW air source heat pump
£1,699
Made for most hot tubs. 7.11kW of heat with a COP of 6.64 in 26°C air, quiet at 54 dB(A), and it works down to -7°C.1
Outdoor Living 12kW air source heat pump
£2,199
More heat for large hot tubs and swim spas: 12.5kW in 26°C air, 55 dB(A), and it keeps working down to -14°C.1
Heat pump questions
Open a question to read the answer. For fitting details, open the installation manual for our 7kW and 12kW heat pumps.
Is a heat pump worth it for a hot tub?
Yes, if you keep your hot tub hot all year. A heat pump turns each kWh of electricity into several kWh of heat by taking warmth from the outside air: about 5.4 kWh on our 7kW heat pump in 15°C air, and about 3 kWh even at -7°C. The hot tub's own electric heater gives about 1 kWh of heat for each kWh it uses.
How much does it cost to heat a hot tub with a heat pump?
Raising 1,000 litres of water by 10°C takes about 11.6 kWh of heat. At 26.32p per kWh that costs about £3.06 with the hot tub's own heater, and about 56p with our 7kW heat pump in 15°C air. Heat lost through the cover and the cabinet comes on top in both cases.
Does a heat pump work in winter?
Yes. Our 7kW heat pump keeps heating in air down to -7°C, with automatic defrost, and still gives about 3 kWh of heat for each kWh of electricity at that temperature. The 12kW works down to -14°C.
What does COP mean on a heat pump?
COP stands for coefficient of performance: the heat a heat pump gives out divided by the electricity it uses. A COP of 5 means 1 kWh of electricity gives 5 kWh of heat. It is higher in warm air and lower in cold air.
Can a heat pump cool a hot tub too?
Yes. Our Outdoor Living heat pumps have a cooling mode that can bring the water down to 8°C, so the hot tub becomes a cool plunge on a hot day.
Sources
- Outdoor Living, Hot tub and swim spa air source heat pump user and installation manual, OLHP07 and OLHP13, technical data, version V20221221.
- Energy Saving Trust, Air source heat pumps, updated 20 October 2026.
- Engineering ToolBox, Specific heat capacity of water, accessed October 2026.
- Outdoor Living, Lagoon hot tub product page (1,000 litres), accessed October 2026.
- Ofgem, Changes to energy price cap between 1 October and 31 December 2026, 26 August 2026.
- Outdoor Living, product pages for the 7kW and 12kW air source heat pumps, accessed October 2026.
Paul Margerison
Managing Director & Founder, Outdoor Living
A hot tub is at its best when it is ready the moment you are. A heat pump keeps it that way all year for a fraction of the electricity.