Heat pumps in existing buildings

Heat pumps in existing buildings


With the release of the government’s Net Zero Strategy in preparation for COP 26 in Glasgow, and the further release of the Heat and Buildings Strategy, addressing the factors driving our impact on the global climate is firmly back on the agenda after arguably taking a back-seat during the COVID-19 pandemic.

Looking at UK emissions from 2019- a more representative year than 2020- buildings account for 30% of our emissions, with 23% of the estimated 454.8 MtCO2e total emissions produced by heating buildings, the majority of which is from homes. It is clear that this is an area of huge importance if the UK is to achieve its Net Zero target by 2050, with the proposed methods to achieve this laid out in the Heat and Buildings Strategy.

Figure 2: UK emissions in 2019

Figure 1- UK emissions in 2019[1]. Source: Heat and Buildings Strategy (2021)

A major aspect of reducing emissions from our buildings is the decarbonisation of the heating systems, namely moving away from traditional fossil-fuel based systems (such as gas boilers) to what will likely be “a mix of low-carbon technologies used for heating, through the electrification of heat for buildings using hydronic (air-to-water or ground-to-water) heat pumps, heat networks and potentially switching the natural gas in the grid to low-carbon hydrogen”.

Heat pumps don’t always receive a good press in the UK, but with the government’s ambition to phase out the installation of new natural gas boilers from 2035, they will undoubtedly become more wide-spread than they are currently. How heat pumps perform in the existing housing stock is an area of real consequence, as if they are to replace traditional gas boilers they must provide occupants with the required level of thermal comfort whilst keeping costs to a minimum.

Heat pumps in existing buildings- what are the issues?


For heat pumps to work most effectively, the building they are heating should be well-insulated. Air-source heat pumps work at lower temperatures than conventional systems, so heat loss through the building fabric and thermal bridges needs to be minimised. Clearly, with existing buildings it is not always possible to improve levels of insulation, with financial and technical constraints barriers for many buildings.

Installation costs

Research conducted by Currie and Brown for the Committee on Climate Change in February 2019[2] estimated that the costs of installing low-carbon heat as a retrofit to an existing gas heated semi-detached home is around £9,000. They also estimate that improving both fabric standards and installing low-carbon heat through retrofit is estimated to result in costs ranging from over £16,000 to more than £25,000 per home- up to five times the cost of achieving the same standards when first constructing the home.

Running costs

Whilst heat pumps are much more efficient that conventional gas boilers, they run on electricity which is considerably more expensive than fossil fuels; the Energy Saving Trust has the average price of natural gas at 4.17p per kWh, whilst the standard rate of electricity costs 16.36 pence per kWh[3]. Part of the issues is that the cost of electricity includes a much greater rate of “environmental/social obligation costs”, with OFGEM data indicating that these costs make up 25.48% of your electric bill, whilst only making up 2.46% of your gas bill[4]. When compared to Europe, the UK ranks below average on gas prices and above average on electricity prices. This may change in the future; the Heat and Buildings Strategy has identified this as an issue and state: “We want to reduce electricity costs so when the current gas spike subsides we will look at options to shift or rebalance energy levies… and obligations… away from electricity to as over this decade”. They intend to launch a Fairness and Affordability Call for Evidence on these options for energy levies and obligations to help rebalance electricity and gas prices and to support green choices, with a view to taking decisions in 2022.

Heat pumps in existing buildings- what are the benefits?


Heat pumps are considerably more efficient than conventional fossil fuel heating systems, with units regularly achieving 300% efficiency, and ground-source heat pumps achieving even up to 400% efficiency. If the government does re-balance the cost of electricity and gas, then the savings from heating a home through heat pumps would be great, which would ultimately drive uptake more than any environmental benefits they have over traditional heating systems.

Lower your emissions

The high efficiency of heat pumps, combined with the ever-decreasing carbon content of electricity from the National Grid means that installing one will reduce your emissions when compared to conventional heating systems, as less kWh are used overall, even if the carbon content of grid electricity is still slightly higher than that of natural gas.


Heat pumps essentially work in reverse to your fridge; by extracting heat from outside and bringing it inside. As a result, heat pumps can provide cooling in the summer, meaning only one system is required for a building and thus can potentially help to alleviate overheating issues.


The government envisages heat pumps as a major technology in heating our homes in the future, and they are likely to be a technology we will all become much more familiar with. Retrofitting heat pumps into existing homes is not without issues; it is how the government helps to address these issues (particularly the high cost of installation, the relatively high cost of electricity vs fossil fuels and how well they perform in existing homes) that will ultimately determine how widely they are adopted.

[1] Source: Heat and Buildings Strategy (2021). UK Government.  

[2] Source: The costs and benefits of tighter standards for new buildings (2019). Currie and Brown for the Committee on Climate Change.

[3] Source: Our data (2021). Energy Saving Trust.

[4] Source: Infographic: Bills, prices and profits (2021). OFGEM.

Article published 21/10/21

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