FEATURE: Is the UK's heat pump goal just hot air?

Rich McEachran

Air-source heat pumps absorb outside heat into a chemical compound, known as a liquid refrigerant, which is then compressed, increasing the temperature (Credit: Shutterstock)
Air-source heat pumps absorb outside heat into a chemical compound, known as a liquid refrigerant, which is then compressed, increasing the temperature (Credit: Shutterstock)

The way our homes are heated is broken and the UK government has a plan to fix it: replace old gas boilers with low-carbon heat pumps and install 600,000 of them a year by 2028.

It’s part of a wider scheme that includes a heat and buildings strategy, which is focused on retrofitting homes with low-carbon heating systems and introducing stricter energy-efficiency rules. The hope is that gas boilers will be phased out and that all new heating systems installed from 2035 onwards will be low carbon. A legally binding target of reducing emissions by 78% by 2035 has also been announced. 

These are ambitious goals that, if achieved, will be a crucial part of the UK transitioning to net zero. Back in 2019, the UK became the first major economy in the world to pass laws requiring the country to achieve net zero by 2050. 

But if heat pumps are to be the future of heating then a number of hurdles will need to be overcome.

Laying the groundwork

Heat pumps can be thought of as reverse air-conditioning systems. They extract heat from outside a home and transfer it inside. There are two main types of heat pumps: ground source, otherwise known as geothermal, and air source. 

Geothermal heat pumps are closed-loop systems that rely on a network of underground polyethylene pipes filled with a mixture of water and anti-freeze to absorb heat from the ground. The mixture is compressed inside a heat exchanger, which extracts the heat and transfers it to the pump, and then on to radiators and a hot-water cylinder. 

Air-source heat pumps absorb outside heat into a chemical compound, known as a liquid refrigerant, which is then compressed, increasing the temperature. The liquid condenses, releasing heat that is then transferred to the heating system. 

Geothermal heat pumps tend to be seen as the better option of the two because the temperature in the ground doesn’t fluctuate as much as in the air. The heating capacity of air-source heat pumps is more likely to drop off during the colder months. 

But geothermal heat pumps require trenches to be dug for laying a horizontal network of pipes or boreholes for a vertical system. The latter, in particular, can be tricky. For starters, homeowners not only need to have a garden but one that is big enough for drilling equipment to carry out the necessary work. The ground condition and geological environment also need to be factored in. 

What about those people that don’t have their own green space? Official statistics show that one in eight UK households has no garden and a fifth of the population lives in flats. In this scenario, air-source heat pumps are ideal. Even then, though, heat pumps in flats work best when a system is installed for all properties at the same time. So, ideally, when blocks are first being built or as part of a retrofit programme. 

“There’s no doubting that heat pumps are a great solution to heating homes in an environmentally friendly way, but the complications of the installation process mean they’re better suited for new-build homes or existing homes that are being heavily renovated,” says Martyn Bridges, director of technical communication and product management at Worcester Bosch, part of Bosch’s thermotechnology division. 

A ground-source heat pump (Credit: Shutterstock)

A ground source heat pump (Credit: Shutterstock)

A retrofit headache

He adds: “There are radiators and pipework to consider. It’s likely these would need replacing in older builds because heating systems need to be large enough to operate at a heat pump’s lower temperature.”

Then there’s the issue of energy performance certificate (EPC) ratings – the colour-coded scale that is designed to reflect a property’s energy efficiency and assigns a score between A (highest) and G (lowest). Most properties in the UK fall between bands D and G. 

Since 2018, private rented properties have had to have a minimum EPC rating of E. Last year, the government outlined green homes proposals that would mean private rented homes would need to be upgraded to band C by 2030. Mortgage lenders have been instructed to have a minimum rating of C across the portfolio of properties on their books. “To bring a home from the lower bands to a band of C or B would cost anything up to £20,000. And that’s before factoring the cost of installing the appliance itself,” says Bridges. “None of the practical considerations are insurmountable, they just add to the cost.”

The shift to electric 

Right now, the cost of installing a heat pump is in the region of £10,000, although a bit lower for air-source ones. The government wants to work with the energy industry to bring the cost down by between 25% and 50% by 2025 and to achieve price parity with boilers by 2030.

Although the government won’t force people to switch from old heating systems to shiny heat pumps, it hopes to encourage them to do so with a £450m boiler upgrade scheme. Grants of £5,000 are available to households from April this year to help cover the cost of replacing them. But the scheme is only set to run for three years and would only provide financial support to 90,000 households. This is hardly likely to make a dent in the government’s 600,000-a-year target. 

It’s not just higher installation costs that could hinder heat pump adoption. Heat pumps rely on electricity to be powered. The lower cost of gas versus electricity could make it challenging to wean people away from boilers. While heat pumps are proven to be efficient – they can produce three to four times more energy than they use – gas is very efficient at heating. (The Committee on Climate Change advocates for hybrid heat pumps that can also use gas at times of peak demand in winter).

Nico van der Merwe, vice-president of Schneider Electric’s home and distribution division, expects that the global transition to electrification over the next decade will help to lower the cost of electricity, encouraging heat pump adoption. Innovation in energy management and sustainability will also be crucial. “It’s not as simple as replacing gas boilers with heat pumps,” he says. 

Cutting the cost of clean heat

Last October, the government announced a £60m innovation programme, Heat Pump Ready, as part of its efforts to drive down the cost of clean heat. The areas the fund is looking to invest in include deploying high-density heat pump systems, such as for high-rise buildings, and upskilling engineering staff and knowledge transfer.

An example of the type of innovation the UK could look to support is from Swedish utility Vattenfall and Dutch heating provider Feenstra. The two parties have developed a high-temperature heat pump that they claim removes the need for insulation or for new radiators to be installed. They have plans to launch in the Netherlands soon and hope to enter the UK in the near future. 

Dutch firm Blue Heart Energy is another example. Its team of engineers has developed a thermoacoustic heat pump that creates a sound wave within a circuit filled with helium which is then used to transfer the gas to a heat exchanger. The technology removes the need for refrigerants and related regulations, meaning in theory that it would be easier to manufacture. The company is hoping to bring it to the mass market in 2023. 

At the end of the day, economies of scale will win out. Even if innovative products come on to the market promising even greater efficiency than geothermal and air-source heat pumps, they won’t take off if the consumer and manufacturing demand isn’t there. 

The heat pumps on the market today may not be cheap to buy, says Bridges, but they’re sold in bulk and use components procured in large volumes, which lowers manufacturing costs.

Installation is still the key driver to bringing down heat pump costs, adds Bridges. There aren’t enough technicians trained to install heat pumps. There are estimated to be 3,000 to 4,000 but up to 40,000 will need to be upskilled if the UK is to achieve its decarbonisation goals, according to British Gas owner Centrica. As more are trained and become experienced in heat pump installations, this should reduce installation times and cost. 

“Heat pumps are always going to be more expensive than putting a boiler in if steps aren’t taken to innovate and train staff,” says Bridges. 

Learning lessons

As the UK inches its way towards its clean energy goals, the government could do no worse than look elsewhere to see how other countries are performing.

Last year, Dr Mari Martiskainen, a senior research fellow at the University of Sussex Business School and co-director of the Sussex Energy Group, explored why Finland has had a broader uptake of heat pumps compared with the UK. 

Reasons for this include older housing stock and a lack of legislation encouraging heat pumps in new builds, says Martiskainen. There have also been limited efforts by utility companies to promote heat pumps to consumers. 

“Finland has a much lower reliance on gas as well as policy support for phasing out fossil-fuel-based heating in the form of tax deductions for installations,” she adds. Adoption has been encouraged by heat pump enthusiasts connecting with each other and sharing their experiences. 

So, what can the UK learn from Finland’s approach? 

“If the UK hopes to get close to its target of 600,000 a year by 2028, it’s going to need long-term policy support, a strong installation chain, and influencers who can educate the public on the benefits of heat pumps,” she says.

Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.

Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.


Professional Engineering magazine

Professional Engineering app

  • Industry features and content
  • Engineering and Institution news
  • News and features exclusive to app users

Download our Professional Engineering app

Professional Engineering newsletter

A weekly round-up of the most popular and topical stories featured on our website, so you won't miss anything

Subscribe to Professional Engineering newsletter

Opt into your industry sector newsletter

Related articles