HyCompact demonstrated the efficiencies of installing a single-unit hybrid heating system, aiming to improve customer acceptability, reduce installation disruption, enhance cost efficiency, and enable smarter control through boiler modulation.
What is the project about?
Domestic energy use accounted for over a quarter of the UK’s greenhouse gas emissions, with up to 75% of household energy consumption used for space and water heating. HyCompact aimed to uncover effective low-carbon heating solutions and reduce emissions across the energy system in pursuit of Net Zero by 2050. Hybrid heating systems, combining an electric heat pump with a traditional gas boiler, emerged as a promising solution to reduce the carbon emissions associated with domestic heating.
How we’re doing it
We worked collaboratively with gas network Wales & West Utilities and technology partner PassivSystems to trial seven single-unit hybrid heating systems in participants’ homes. Once installed, we closely monitored their performance to collect comprehensive operational data, assess network impacts, and explore flexibility opportunities. We also engaged with participants throughout the trial to gather feedback on their experience and identify ways to improve the customer journey.
What makes it innovative
The units represented a new type of hybrid heating system that combined a gas boiler, an electric air-source heat pump, and smart control software into a single, compact unit. Designed to be wall-mounted in place of a conventional gas boiler, they could intelligently switch between gas and electricity based on real-time cost and carbon emissions, optimising both efficiency and environmental impact.
The HyCompact trial built on the earlier Freedom Project, previously led by Wales & West Utilities, which tested hybrid heating systems—consisting of a separate gas boiler and external air-source heat pump—in 75 homes in Bridgend, South Wales. HyCompact aimed to advance this concept by integrating the components into a single unit to further reduce installation complexity and improve customer acceptability.
What we’re learning
HyCompact provided a valuable opportunity to share learnings across both the gas and electricity sectors. Achieving Net Zero carbon emissions by 2050 will require true whole-system trials and cross-sector collaboration, and this project served as a strong example of that approach. The trial delivered several key insights:
Key Learnings from the HyCompact Project
1. Carbon Savings
Compact Hybrid Heating Systems (CHHS) demonstrated significant potential to reduce carbon emissions. The systems achieved heat pump usage levels of approximately 40–58%, translating to CO₂ reductions of 30–48% compared to a conventional gas boiler. This equates to an annual reduction of over 1 tonne of CO₂ per home.
Analysis of UK housing archetypes suggested that up to 14 million homes could be suitable for CHHS installations based on available space and heating demand.
2. Potential Running Cost Savings
Due to the current cost disparity between gas and electricity (electricity being roughly 4 times more expensive per kWh), the trial observed only marginal cost savings of around 4%, achieved in one home with a high-performing heat pump (high Coefficient of Performance, or CoP).
Overall, homes in the trial showed running costs broadly comparable to a conventional gas boiler, with an average CoP of 2.8. However, greater cost savings could be achieved by optimising CHHS operation in response to Time-of-Use (ToU) tariffs or flexibility signals.
3. Enabling Effective System Planning
HyCompact demonstrated that a smart-controlled CHHS can flexibly switch between fuel sources in response to external signals, such as grid stress or future periods of hydrogen availability.
The system was successfully optimised to avoid peak Distribution Use of System (DUoS) charging periods (4–7 pm), delivering additional savings. Independent analysis by Imperial College London estimated that such systems could deliver £100 in annual energy system cost savings per installation.
4. Understanding User Experience
Customer feedback indicated promising user acceptance:
79% of surveyed participants were attracted to the CHHS design and its perceived benefits.
However, only 16% were initially aware of heating technologies beyond conventional gas boilers.
Some households reported noise issues when the heat pump was operating. This was addressed by retrofitting a noise vibration kit, including a specially adapted wall-mounted bracket.
5. Installation Benefits – Gas-Safe Compatible
CHHS units installed during the project integrated the heat pump and gas boiler within a single casing. This design eliminated the need for F-gas handling, allowing installation and commissioning by Gas Safe-registered engineers without requiring MCS accreditation.
This is particularly valuable for the installer supply chain during a time of rapid change, supporting scalability and workforce readiness for hybrid system deployment.
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