The decarbonisation of heating is one of the major challenges facing the UK as it aims to meet its 2050 Net Zero targets.

A transition from gas based central heating to electric heating is widely believed to be one of the critical solutions for domestic heating with heat pumps as one of the major enabling technologies for the electrification of heat.

However, there are concerns regarding (1) the ability of a heat pump to deliver acceptable comfort levels in a real-world environment without significant retrofit to improve thermal performance of the home into which they are installed, and (2) the cost of operating a heat pump compared to a gas boiler.

(1) Trials in Energy Systems Catapult’s Living Lab over the winter of 2019/20 demonstrated that it is possible for consumers to achieve desired comfort levels by simply replacing a gas boiler with a heat pump and without further upgrades.

(2) However, there had been limited research to date of a direct cost comparison between a gas boiler and a heat pump in heating a home under real world conditions with real consumers.

Key points

Energy Systems Catapult utilised five homes in our Living Lab that have hybrid heating systems installed, consisting of a gas boiler, a heat pump and a bespoke zonal heating system managed from a central cloud-based software application.

With this facility, a home where the gas boiler was providing some of the heating could be switched to having all of the heating provided by a heat pump simply by setting a software switch in the cloud. As there was no need to visit the house, the impact on the resident was minimal, thereby reducing any impact due to changes in behaviour.

By comparing the cost of the energy used by the heat pump with an estimate of the cost of using the boiler to produce the same amount of heat energy, it was found:

• In one home. the cost of using a heat pump was almost cost neutral but in others, a total increase in energy costs ranged from 4% to 64%.
• For domestic property supplied with electricity and gas from the grid, the financial benefit is primarily influenced by the difference in energy supply tariffs.
• To make a heat pump to be cost effective the cost of electricity must be less than 3.2 times the cost of gas. For the five trial participants considered in this research, the average unit price for electricity was 4.4 times that of the average unit price for gas.
• Due to this difference in electricity and gas unit rate, a Coefficient of Performance of over 4 would be required to make a heat pump cost neutral. In our five home trial, one consumer had an electricity-favoured tariff which produced the cost neutral result.

These findings have been made with heat pumps set to deliver 55C flow temperatures, with no modifications being made to the heating system to make it more suitable for a heat pump or any optimisations being made to the heat pump. It has also been assumed that the gas boiler would be 90% efficient.

Initial analysis suggest that the heat pumps may be operating below expected efficiencies so further cost reductions may be possible. The results have been obtained from only 5 homes over a very limited period in one heating season. Further extension and replication would be recommended.