How do heat pumps work?

As we seek ways to lower carbon emissions in our homes, we need to switch from heating that relies on high-carbon fuels to cleaner, low- or zero-carbon alternatives. Here we explain how heat pumps work and their potential to help us transform how we heat our homes and businesses in the future.

Heat pump is a term you’re going to be hearing a lot of from now on. That’s because heating our homes and businesses accounts for 37% of UK emissions and 85% of our homes are heated with gas. Switching to cleaner, low-carbon options will play a critical role in tackling climate change.

In the run up to net zero 2050, we’re going to see a transformation in the way we heat our homes. The challenge is sizable – over 20,000 homes every week will need to switch to a low carbon heat source between 2025 and 2050.

Many different heating technologies are needed to reach net zero and one of those is heat pumps.

What is a heat pump?

In simple terms, 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.

They’re set to become much more common in the future. According to government figures from 2020, there are currently around 1.7 million gas boiler installations every year. But, by the mid-2030s, the aim is for all newly installed heating systems to be low-carbon or have the potential to be converted easily to a clean fuel supply.

Recently, in the Energy White Paper 2020 the Government outlined its ambition to increase the installation of heat pumps from 30,000 a year to 600,000 a year by 2028, to accelerate the decarbonisation of heating.
 

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

How exactly does a heat pump work?

When it comes to heating, think of a heat pump as a refrigerator working in reverse – instead of keeping your veg and dairy products cool, it’s warming your home using a refrigerant, which can evaporate into gas and condense into liquid.

A heat pump works like this:

  1. 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. It’s important that good energy efficiency is installed in homes so that heat pumps can work at their best.

What’s the difference between air-source pumps and ground-source pumps?

Air-source heat pumps

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.

Ground-source heat pumps

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.

What is a hybrid heat pump?

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.

What do heat pumps have to do with meeting net zero by 2050? Are they environmentally friendly?

Yes, taking heat from the air or ground in a constant cycle is sustainable and renewable, with low or no CO2 emissions.

Don’t heat pumps use electricity?

Yes, 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 efficiently extract a greater amount of heat energy from the surrounding environment than the energy they consume to create heat.

Also, electricity generation is progressing towards net zero and has already decarbonised by 66% in the last seven years. Last year (2020) was the greenest year on record, with renewable energy like solar and wind increasingly powering the system.

Can heat pumps be used as air conditioners too in warm weather?

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.

What are the other advantages of heat pumps compared to a traditional heating system?
  • The feel-good factor of reducing carbon emissions by using a heating system that is three times more efficient than a gas boiler.
  • Tried and tested technology that reduces carbon emissions.
  • Installing a heat pump may qualify you for the Renewable Heat Incentive, the Government financial incentive scheme that pays you quarterly for seven years for generating your own heat through renewable technology. A successor scheme, the Clean Heat Grant, is due to launch in 2022 to support the installation of heat pumps. You can also apply for the Green Homes Grant, which can be used for energy efficiency and low-carbon heating before March 2022.
Are there any disadvantages to heat pumps?
  • Heat pumps may not be suitable for all buildings, particularly older ones. Energy efficiency measures need to already be in place, such as roof and cavity wall insulation, and radiators may need to be increased in size.
  • There may be noise from the pump condenser.
  • Installing ground source heat pumps requires a large garden with easy access for digging, with some disruption.

Will heat pumps be the future home heating number one choice?

According to the government’s Energy White Paper, fewer than one per cent of homes in England currently use a heat pump. So clearly the pace of change and scale needs to pick up in this home energy transformation. There is no ‘silver bullet’ for home heating, as different low-carbon heating solutions may be required for different types of buildings and locations. Heat pumps are expected to make an important contribution to decarbonising heat.

Our own research, which investigated what matters to consumers in the transition to lower-carbon heating, has highlighted the knowledge gap between good intentions and daily lives; 93% of people said climate change was a serious or very serious issue but only 5% identified heat as a main contributor to the UK’s carbon emissions.

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That said, heat pumps are set to become one of the new clean alternatives to fossil fuels alongside biomass boilers, which burn plant-based materials like wood pellets, hydrogen boilers and heat networks for densely populated areas, like the one our Innovations team is currently prototyping.

It’s likely that homeowners will be offered a mosaic of solutions, including heat pumps, rather than a one-size-fits-all decarbonised heating solution.

Our research found that key to the home heating transformation will be:

  • keeping the reliability and comfort we’ve all come to expect
  • transparency on upfront and ongoing costs
  • future financial incentives, such as the current green grants and lower energy bills
  • preparing suppliers, installers and equipment manufacturers for the clean home energy transition
  • ensuring consumers get the right advice when considering future heating needs
  • that any heating solution needs to be installed with the right level of energy efficiency measures and smart operation.
Cuddly duck and socks on radiator

Read more about the future of heating and our recommendations
 

Heating our homes in a Net Zero Future: Understanding what matters to consumers

 

Energy explained