About heat pumps

About heat pumps

What is a heat pump?

A heat pump is a device that can provide heating, cooling and hot water for homes, businesses and even for industry.

Heat pumps take energy from the air, ground or water and turn it into heat.  In reverse, they remove heat energy, like an air conditioner.

This makes them a highly efficient, renewable, sustainable way of heating and cooling.

What’s more, they work well in nearly all types of climates.

This is due to what is known as the refrigerant cycle.

about pumps

How a heat pump works: the ‘refrigerant cycle’

The ‘refrigerant cycle’ has four phases: evaporation; compression; condensation; expansion.


A heat pump takes in heat or cold from the air, water or underground and transforms it into heating or cooling for your building or water.

Sources include ambient air, exhaust air, underground heat, groundwater and water.

The energy from these sources is infinite, meaning it is renewable.

This energy makes up about 80% of the energy needed.

The heat pump captures the heat from the ground, or the air or water. This heat is then used by the heat exchanger, known as the evaporator, to turn the refrigerant in the heat pump into gas.


The refrigerant gas then reaches the heart of the heat pump: the compressor. The compressor compresses the refrigerant gas to a high pressure, which leads to a rise in temperature.

Why this works: High pressure heats up gas, just like a bicycle pump that heats up when you are using it.

To drive the compressor, additional energy is needed. This can come from electricity, gas or thermal energy. This makes up about 20% of the total energy needed to run the heat pump. If green electricity is used, for example from solar or wind energy – then the heat pump uses 100% renewables and is carbon neutral.


On the discharge side of the compressor, vapour which is now hot and highly pressurised passes through the second heat exchanger, called the condenser. This heat exchanger allows the refrigerant to release heat into the heating system for the house. As a result, the refrigerant then turns back from a gas into a liquid state.

The heat coming into the house can do so through an air system, like an air conditioning unit, or a water-based system like floor heating or radiators, known as ‘hydronic’. The indoor unit can also contain a hot water storage tank.


The condensed refrigerant then passes through a pressure-lowering device, known as the expansion valve. The now low-pressure liquid refrigerant can then begin the cycle again.

Types of heat pumps

Air source heat pumps

Air source heat pumps use the energy in outside air or air from a ventilation system for heating, cooling and heating water. They can be installed entirely inside or outside the house. Or, you can have a system with one unit inside the building and one outside.

Water source heat pumps

Water source heat pumps use the energy stored in ground water, surface, or sea or sewage water. The heat pump takes heat from the water and makes it available for heating, cooling and preparation of hot water. Water source heat pumps are particularly efficient because water is a very good energy carrier.

Ground source heat pumps

Ground source heat pumps use the energy stored in the ground. They extract heat from the ground either by a vertical or horizontal collector.

Electrically and thermally driven heat pumps

Many heat pumps use electricity to drive the compression cycle – meaning to heat up the energy from the air, water or underground a bit more. The heat pump can be plugged in and use renewable electricity.

Thermally driven heat pumps use heat or an engine to drive the compression cycle instead.
There are three main types of thermally driven heat pumps. Gas sorption heat pump (GAHP) and thermal compression heat pump (TCHP) are both covered by the standard EN 12309 and gas engine heat pump (GEHP) is covered by the standard EN 16905.

Where can heat pumps be used?

Heat pumps can provide CO2-free heating and cooling and hot water in all types of home, and for commercial spaces like hospitals and offices.

Heat pumps can also provide heat for industry. European industries like steel, chemicals, paper, food, and tobacco use a huge amount of energy – about a quarter of the EU’s consumption.

District heating allows heat to be produced in one place and then distributed via insulated pipes to houses and businesses.

The heating and cooling sector is responsible for 51% of the final energy demand in Europe and for 27% of its CO2 emissions. Decarbonising society is impossible without decarbonising heating and cooling.


Find more in our Heat Pumps in Europe – Key Facts & Figures.

Read our Frequently Asked Questions (FAQ).

Interested in costs? Use the My Heat Pump tool to calculate and compare.


Heat pumps: How they work and why they matter
Large heat pumps and industrial uses
The history of heat pumps – the Swiss Federal Office of Energy