What are heat pumps and how do they work?

If you know one thing about heat pumps, it’s probably that they’re the latest, greenest heating technology. But because heat pumps are so new, many of us don’t know the ins and outs. That’s why we’re going to cover the question ‘How do heat pumps work?’ and help you decide if a heat pump could work for you.

Heat pumps feature in the UK’s path to net zero by 2050, as detailed in the Heat and buildings strategy. This is because heat pumps can run on renewable energy from the electricity grid. They're also very good at turning electricity into heat — typically three times more efficient than a gas boiler. As we expect to see many more heat pumps soon, it’s a good idea to know how they work.

Heat pumps fall into two categories: ones that take heat from the air, or from the ground. These are known as ‘air source’ and ‘ground source’ heat pumps. There are pros and cons to each type, depending on what your home or property is like.

It’s worth noting that a heat pump alone may not be enough to meet all your heating requirements. This depends on your home or property and how much demand there is for heating there. You can overcome this by having an electric boiler, immersion heater or central heating boiler in addition to the heat pump.

The basic idea of all heat pumps is the same: they work like a fridge, but in reverse. First a special substance called a refrigerant picks up some heat from outside the house. The heat pump then compresses this refrigerant, which makes it much hotter. That heat then moves inside your house, the refrigerant cools down and the cycle repeats.

So, unlike other forms of heating, you're not burning fuel in a heat pump. It just takes the natural heat from outside and compresses it to raise its temperature for heating.

Here’s a more detailed explanation of how a heat pump works:

• Air or water outside your home moves over the heat exchanger inside the pump.
• This heats up the refrigerant liquid in the heat exchange, making it evaporate.
• The refrigerant, now a gas, travels into the compressor.
• The compressor pressurises the gas, increasing its temperature.
• This gas moves over a second heat exchange, where it turns back into a liquid as it transfers its heat to your home’s heating system.
• The cycle begins again.

To answer the question ‘Do heat pumps save you money?’ we need to know a few factors:

1. The difference in cost between fuel and electricity at the time
2. The heat pump’s efficiency compared to other heating systems — this is especially important when we have extreme cold weather like the Beast from the East
3. How your central heating system is designed
4. The average ground or air temperature where you live
5. The cost of installing a heat pump compared to other heating types

Gas heating is cheaper than electricity on average at the moment. We can’t predict future events, but it’s expected that gas will be subsidised less and then gas prices will rise. This would make gas boilers less attractive in the long term.

On top of this, heat pumps are much more efficient than any other heating type. This means they have the potential to make electric heating as cheap as gas. What’s more, heat pumps are low-maintenance and can last twice as long as a boiler. Of course, this depends on them being installed, serviced and maintained to the manufacturer’s instructions.

On the downside, heat pumps are more complicated and costly to install than conventional boilers. The UK government aims to make this less costly for households by covering some of the installation costs. In the case of ground source heat pumps, the property’s size and location can limit your installation options and the usable heat output.

The UK government is running the Boiler Upgrade Scheme from 2022 to 2025. The scheme aims to encourage more people in England and Wales to install low-carbon heating systems, like heat pumps. There are other ways of funding this in Scotland and Northern Ireland — see Home Energy Scotland or NI Energy Advice.

The scheme can provide up to:

• £5,000 towards buying and installing an air-source heat pump
• £6,000 towards buying and installing a ground-source heat pump

You can apply for homes and other small buildings, needing up to a maximum heating capacity of 45kWth (kilowatt-thermal). This covers most homes and buildings of a similar size to the average house.

The property will need an energy performance certificate (EPC), with recommended loft or cavity wall insulation already in place. You can find out more about what properties are eligible for the Boiler Upgrade Scheme.

The best heating system for you depends on your property’s size, age, location in the country and what you can afford. The main points to compare fall into four categories:

• Installation costs: heat pumps are currently more expensive to install.
• Running costs: heat pumps may become cheaper than gas to run.
• Lifetime and maintenance: heat pumps need less maintenance and last longer.
• Environmental: heat pumps can run on entirely renewable energy sources.

Let’s look at each of these points in more detail.

Heat pumps are a very efficient type of heating system because they produce more heat than the energy they use. A gas boiler is around 90% efficient, meaning that up to 10% of the gas is wasted. A heat pump is about 300% efficient, meaning that it triples the energy that goes in. It does this by recovering latent heat in the ground or air, depending on the system type.

At the same time, electricity is currently about four times more expensive than gas, on average. In the future, increases to renewable electricity supplies will lower the cost of electricity. In this way it’s expected that gas prices will increase while electricity prices go down. So overall, it may be that heat pumps and gas boilers will cost about the same to run eventually.

A heat pump doesn’t have to burn fuel or deal with the high temperatures a gas boiler does. For this reason, heat pumps can have a lifetime of about 30 years. Meanwhile, a gas boiler will typically last around 10 years before needing to be replaced.

Heat pumps are also easier to maintain than gas boilers. Because of the safety risks of gas, your boiler needs a specialist Gas Safe registered engineer to service it. Being less dangerous, a heat pump doesn’t need that level of training when servicing it.

Gas boilers also carry more risk for you. When faulty, they have the potential to leak carbon monoxide into your home, which can be deadly. This means you’ll need to buy carbon monoxide detectors. While rare, there's also the risk of fire and explosion from faulty gas boilers.

Before deciding if a heat pump is right, you need to check that your home is suitable for one. Heat pumps provide a lower but more constant heat than gas boilers. You may need to make some changes to your home for this heating to work at its best.

It’s worth considering a heat pump if:

• Your home already has good wall and loft insulation
• You have suitable space outside your house for the heat pump unit
• Your windows are double or triple glazed
• You’re prepared to have larger radiators installed to provide the same level of heat

For more detail, you can check if your home is suitable on the government’s heat pump check service.

If your home is suitable for a heat pump installation, the next step is to look into the process and costs. To benefit from the government’s Boiler Upgrade Scheme you’ll need to use a Microgeneration Certification Scheme (MCS) installer. These installers have the right skills and use high-quality products. The government can help you find a certified heat pump installer.

Before arranging installation, you’ll need to check if the project needs planning permission. You can ask the installer or your local council’s planning authority. It’s also best to check with your home insurance provider that they'll cover the work on your property.

When talking to potential installers, you can ask them:

• How long will the installation take?
• Can I make changes to my heating that will reduce my bills or let me get a smaller heat pump?
• How often will the heat pump need servicing?
• Will I need a secondary heat source, such as solar, a boiler or immersion heater, for high demand and seasonal cold weather?