How Heat Pumps Work · 4 lessons
How does a heat pump work?
A heat pump doesn't burn anything to make heat. It uses electricity to move heat that's already outside, in the air or the ground, into the home's heating water.
Have a go
0What does the compressor do in heating mode?
Tap an answer
Moving heat, not making it
Even cold outdoor air holds heat. A refrigerant inside the heat pump soaks it up, a compressor squeezes the refrigerant so it gets hotter, and that heat passes into the water going round the radiators. A fridge does the same job the other way round.
Air, ground or water
The name says where the heat comes from, not where it goes. An air source heat pump draws on outside air; a ground source one on pipes buried in the ground or a borehole; a water source one on a lake or river.
COP and SCOP
COP compares heat out with electricity in at one moment: 8 kW of heat from 2 kW of electricity is a COP of 4. SCOP is the same idea averaged over a whole heating season, so it's the better guide to running costs. Both go down as the water gets hotter.
Monobloc or split
A monobloc has all its refrigerant sealed inside the outdoor unit, so only water pipes come into the house. A split system has refrigerant pipes between an outdoor and an indoor unit. The refrigerant side is specialist work, not water-side plumbing: plumbers hand it over.
Key numbers
- COP 4
- 8 kW of heat out for 2 kW of electricity in, at one set of conditions.
Common mistakes
- Thinking a heat pump makes heat from electricity, like an electric heater.
- Quoting a COP from one mild day as if it were the whole year's SCOP.
- Treating the refrigerant pipes of a split system as ordinary plumbing.
The lessons this guide comes from
- Moving heat, not making it
- Air, ground and water sources
- COP and SCOP
- Monobloc or split
Keep learning
- Heat pump topics
- Heat pumps: learn the water side
- COP (coefficient of performance)
- SCOP (seasonal COP)
- Monobloc heat pump
- Split system
- Refrigerant
- Air source heat pump
- Heat pump practice questions
- Heat loss: how big a heat pump does a house need?
- Do radiators work with a heat pump?
- Hot water with a heat pump
- Commissioning a heat pump system
- Heat pump grants and MCS, nation by nation
Sources
Sources checked 31 October 2026. Guidance, grants and official pages can change.
- Government guidance: Qualifications to work with F gasIn Great Britain, people working on equipment containing F gas, including heat pump systems, need their own F-gas qualification.
- DAERA: Fluorinated greenhouse gasesNorthern Ireland's F-gas rules, which follow the EU F-gas law and are run by DAERA.