Pool heat pumps: your questions answered

An air source heat pump takes heat from the air and puts it into your pool water, for a fraction of the cost of other ways of heating.

  • Up to 80% cheaperTo run than a gas boiler
  • COP up to 17Inverter models at A27/W27
  • Whisper quietAs low as 30dB
  • Down to −20°CAll season models
A Poolex Silverline pool heat pump

How they work

A fan draws air over the heat pump’s evaporator, and the refrigerant circulating inside absorbs heat from the air. The compressor then raises its temperature further, and the heat is transferred into your pool water.

A heat pump still works when the air is cold: modern heat pumps have an automatic defrost function to stop the evaporator freezing over.

FAQs

It takes energy from the outside air and transfers it to your pool water:

  1. A fan draws outside air across the evaporator.
  2. The refrigerant in the evaporator absorbs heat from the air and becomes a gas. It’s colder than the air, so it still absorbs heat at zero degrees and below.
  3. The compressor squeezes the gas, making it very hot.
  4. In the condenser the hot gas gives its heat to your pool water.
  5. The refrigerant turns back into a liquid and the cycle starts again.
Swimming Pool Heat Pump - How It Works Diagram

The coefficient of performance, or COP, is the heat a heat pump puts out for each 1kW of electricity it uses. A COP of 6 means 6kW of heat for every 1kW. The higher the COP, the lower the running cost.

Its compressor speeds up and slows down as needed, so it reaches your temperature faster and holds it more efficiently than a fixed speed model, which switches on and off. Ours reach a COP of up to 17, are up to 30% more efficient, quieter, and soft start, so they don’t draw a surge of current when they switch on.

Our heat pumps use R32. From 2027 they’ll use R290, a natural refrigerant that is fluorine free, with a global warming potential (GWP) of 0.02, compared with 675 for R32.

Running costs

A heat pump is the cheapest way to heat a pool. Traditional heating methods have a COP of around 1: for each 1kW of energy they use, they put out roughly 1kW of heat. Even the smallest heat pump outputs 3 to 6kW of heat for every 1kW it uses, depending on the air temperature:

  • At 25°C, 5 to 6kW
  • At 15°C, 4 to 5kW
  • At 10°C, around 3kW, still cheaper than any other way

FAQs

A larger heat pump uses more power, but it heats your pool faster, so it uses almost the same energy overall. Being quicker, it can also do its work in the warmest part of the day, when it runs most efficiently.

Keep your pool covered when you’re not using it: 80% of its heat loss is from the surface. It matters most for above-ground pools. If yours didn’t come with a cover, a solar cover is well worth it.

Choosing a size

Our sizing guide suggests the right heat pump for your pool. We also take into account how and when you swim, the temperature you want and your pipework, so call us on 01284 658770 if you’d like advice.

FAQs

  • Length × width × average depth, in metres
  • Average depth is the shallow end plus the deep end, divided by two
  • For Roman end and shaped pools, measure at the longest and widest points
  • For above-ground pools we double the volume, as they lose more heat

Many customers do. It costs more at first, but gives a longer swimming season or warmer water, and costs almost the same to run.

In colder air a heat pump puts out less heat while your pool loses more. The balance point is where they meet: below it, it can’t keep your pool at temperature. A larger heat pump moves the balance point, for warmer water or a longer season.

Graph showing a heat pump's output falling and a pool's heat loss rising as the air gets colder, meeting at the balance point

Installation

Heat pumps go outside, on a solid, level base, with space around them for air to flow: fresh air matters more than sunshine.

Horizontal models need 300mm behind, 700mm either side, 500mm above and 2.5m in front. Vertical models need 800mm to 1m behind and either side, and 2m above. Check the manual for your model, as distances can vary.

The heat pump needs its own electrical supply, wired by a qualified electrician, and enough water flowing through it from your filter pump.

FAQs

Wiring must be done by a qualified electrician, on its own circuit with a motor-rated MCB (type C or D) and the fuse and cable size in the manual. Not following the manufacturer’s guidelines could invalidate your warranty.

We don’t recommend it with a sand filter: the heat pump switches off once the pool is warm, which could cut your filtration short, and you couldn’t backwash. Give the filter pump its own supply; the heat pump switches itself on and off with the water flow.

Three valves and pipework in the return after the filter pump, before any dosing. It controls the flow through the heat pump and lets you service or winterise it without stopping the flow to your pool.

Heat pumps need a minimum flow rate, so you may need to upgrade your pump or filter. Old filter sand often causes low flow: replace it every two to five years. If you’re not sure, talk to us first.