How do heat pumps work?

A heat pump takes heat from the ground or air around a building and increases it to a temperature that keeps homes and businesses warm inside.

Find out about the different types of heat pumps, how they work and why they could help us to tackle climate change at home.

Why do we need heat pumps?

Around 40% of global emissions come from buildings and most of these result from the ways we heat our homes and businesses. Using natural gas for heating contributes almost 20% of the UK’s greenhouse gas emissions and in the Northeastern US it’s around 35%. Switching to cleaner, low-carbon options will play a critical role in tackling climate change.

To lower our carbon emissions and reach net zero, we need to switch from heating that relies on high-carbon fuels to cleaner, low- or zero-carbon alternatives. One of these alternatives is heat pumps.

How a heat pump works

A heat pump works a bit like a refrigerator in reverse; instead of keeping your food cool, it’s warming your home using a refrigerant, which can evaporate into gas and condense into liquid.

  1. For National Grid's 'How do heat pumps work?' article

    The source of heat – air outside or warmth from the ground – is blown or pumped over the heat exchange surface of the exterior part of the heat pump.

  2. This heat (although cold in comparison to a centrally-heated home) is warm enough to cause the special refrigerant liquid to evaporate and turn into a gas. 

  3. This gas then moves through a compressor, which increases the pressure and so causes its temperature to rise.

  4. The gas (now heated) is passed over the internal heat exchange surface. This heat can then be either blown around the interior or transferred into a central heating or hot water system.

  5. The gas falls in temperature as the heat is transferred into the home and it subsequently returns to a liquid state.

  6. The cycle of reverse refrigeration repeats until your home or business reaches the required temperature setting on your thermostat.

As the ground and air outside always contain some warmth, a heat pump can supply heat to a house even when it’s cold outside. For heat pumps to work at their best, it’s also important that good energy efficiency is installed in the home, such as effective insulation.

There are different types of heat pumps: air-source, ground-source and hybrid heat pumps.

How does an air-source heat pump work?

An air-source heat pump takes heat from the air and boosts it to a higher temperature using a heat pump.

There are two main types of air-source heat pumps – air-to-water and air-to-air. Air-to-water heat pumps take heat from the outside air and feed it into your wet central heating system (similar to existing gas central heating). As the heat produced is cooler than that from a conventional boiler, you may need to install larger radiators or underfloor heating in your home to make the most of it. Air-to-water heat pumps may be best suited to new-build properties or those that are energy efficient.

Air-to-air heat pumps take heat from the outside air and feed it into your home through fans. This type of system can be used for heating but can’t produce hot water.

How does a ground-source heat pump work?

A ground-source heat pump system harnesses natural heat from underground by pumping water through it in pipes. The heat pump then increases the temperature and the heat is used to provide home heating or hot water.

The pump performs the same role as a boiler in a central heating system. But it uses ambient heat from the ground, rather than burning fuel to generate heat. 

Ground-source heat pump systems are made up of a ground loop (a network of water pipes buried underground; the larger your home and heating needs, the larger the loop) and a heat pump at ground level.

A mixture of water and anti-freeze is pumped around the ground loop and absorbs the naturally occurring heat stored in the ground. The water mixture is compressed and goes through a heat exchanger, which extracts the heat and transfers it to the heat pump. The heat is then transferred to your home heating system.

You can then use this heat in a radiator, for hot water or in an underfloor heating system.

How does a hybrid heat pump work?

A hybrid heat pump system, also called a dual energy system, integrates a heat pump (air source or ground source) with your traditional gas boiler heating system, or potentially even your hydrogen boiler in the future.

A hybrid heating system monitors the temperature outside and automatically chooses the most energy efficient option to keep your home consistently warm and your hot water running.

How can heat pumps reduce our emissions if they run on electricity?

Heat pumps do use electricity, but they can produce two to three times more heat output than they consume in electricity input.

Heat pump systems are designed to extract a greater amount of heat energy from the surrounding environment than the energy they consume to create heat.

Also, electricity generation itself is progressing towards net zero. Renewable energy sources like solar power and wind energy are increasingly powering our systems, meaning the electricity that’s used to power heat pumps is becoming cleaner.

Can heat pumps also be used as air conditioners?

Yes, the heat pump cycle is fully reversible and heat pumps can provide year-round climate control indoors – warming in winter and cooling in summer.

The future of heat

Did you know that heating is one of the biggest emitters of the greenhouse gas CO2 across the world? So in order to reduce our carbon emissions and tackle climate change, we need to change the ways we heat our homes and businesses.

Watch the video