A swimming pool heat pump is the most cost-effective way to heat a pool. By extracting free heat from the outside air and transferring it to the water, a heat pump delivers far more energy than it consumes in electricity. This guide explains how heat pumps compare to other heating methods, how they work, and what the running costs look like.
Heating Options Compared
Several options exist for heating a swimming pool. A heat pump uses free energy from the air and is the most efficient choice for outdoor pools. Gas and oil boilers deliver consistent output regardless of air temperature and suit large indoor pools, but running costs are typically double those of a heat pump. Electric heaters are cheap to buy but expensive to run — 1 kW in equals 1 kW out, with no amplification. Heat exchangers borrow heat from an existing boiler circuit but don't generate heat themselves.
| Method | Efficiency | Running cost |
|---|---|---|
| Inverter heat pump | Up to 14× (COP 14) | Lowest |
| Standard heat pump | 5–7× (COP 5–7) | Low |
| Gas boiler | ~90% (COP ~0.9) | Medium |
| Oil / propane | ~85% (COP ~0.85) | Medium-high |
| Electric heater | 100% (COP 1) | High |
Why Heat Pumps Cost Less to Run
An electric heater converts 1 kW of electricity into 1 kW of heat. A standard heat pump converts 1 kW of electricity into 5–7 kW of heat by capturing free energy from the air. An inverter heat pump running at reduced load can achieve up to 14 kW of heat output per 1 kW consumed.
In practical terms, this means a heat pump costs roughly half the amount of natural gas, a third of the cost of oil or propane, and a fifth of the cost of electric resistance heating to achieve the same result.
Inverter Technology
Inverter-driven heat pumps use variable-speed compressors and fans. Rather than switching fully on and off, they continuously adjust their output to match the pool's demand. Once the water has reached the target temperature, the unit drops to around 25–50% of its maximum output to maintain it. At these lower outputs, the COP reaches its highest levels.
The benefit is not just efficiency. Inverter units also operate more quietly, run with less vibration, and have fewer abrupt on/off cycles, which reduces wear on the compressor over time.
Running Cost Example
Based on a 12 kW heat pump running for 4 hours per day at a COP of 6, with electricity at 24p per kWh: the heat pump uses 2 kW of electricity per hour, costing approximately £1.92 per day. A comparable electric heater would cost over £11 per day to deliver the same heat output.
Actual running time depends heavily on weather conditions. On warm days with a pool cover in place, the heat pump may not need to run at all. In cooler conditions below 15°C, it may run for 4–8 hours per day.
Key saving tip
A good solar pool cover reduces heat loss by up to 70%, particularly overnight. Fitting one is the single highest-impact action you can take to lower running costs — it works alongside the heat pump, not instead of it.
Choosing the Right Heat Pump
The correct size of heat pump depends on the pool volume, the desired water temperature, the lowest ambient temperature expected during the swimming season, and how well the pool is covered. We offer a free sizing service — send us your pool dimensions and seasonal usage plans and we'll recommend the right model.
Titanium heat exchangers are an important feature to look for. Titanium is resistant to the corrosive effects of chlorinated pool water, which means the heat exchanger will last considerably longer than copper or mild steel alternatives.
Other Heating Options
Gas and oil boilers are better suited to large indoor pools where heat is needed for both the water and the air. Their advantage is that their output does not vary with the outside temperature. For outdoor pools, however, the running cost of a gas boiler is typically around twice that of a heat pump.
Electric heaters are suitable for very small pools or as emergency backup heating. Their low purchase price is offset by significantly higher running costs compared to a heat pump.
Heat exchangers are used when another heat source, such as a central heating boiler, is already available on site. They transfer heat from the boiler circuit into the pool water. They do not generate heat themselves and are dependent on the efficiency of the primary heat source.
Free sizing advice
Not sure which heat pump is right for your pool? Send us your pool size, where you're based, and how long you want to swim each year. We'll recommend the right model and spec the correct pipe connection kit.