Hybrid heating systems: a pragmatic route to Net Zero in non-domestic buildings
The decarbonisation of heat in the UK’s non-domestic building stock remains one of the most technically complex and operationally sensitive challenges facing commercial heating engineers.
Non-domestic buildings account for approximately 4% of total UK greenhouse gas emissions and around 22% of emissions from the overall building stock. With a significant proportion of existing heating systems approaching end-of-life, the sector faces a critical window for intervention, as Steve McConnell, Director of ICOM, discusses.
The recently announced Buildings Standards (FHBS), due to come into force in March 2027, signals a decisive shift toward low carbon heat, electrification and higher energy performance expectations. For engineers and specifiers, the question is no longer whether systems in new-build properties must decarbonise, but how to do so in a way that is technically viable, economically deliverable and aligned with operational realities.
Hybrid heating systems that combine electrically driven heat pumps with gas-fired boilers offer a compelling and pragmatic solution but this option has been frowned on by policy-makers. This has prevented a combined pragmatic approach but designers are finding that it is possible to provide new buildings with an all-electric, low carbon heating system. When we turn our attention to decarbonising existing buildings the challenges become even greater.
The challenge of full electrification
While heat pumps are widely recognised as a cornerstone of low carbon heating strategies, their application in non-domestic retrofit scenarios is often constrained by the characteristics of existing buildings and systems.
Many commercial buildings were designed around high-temperature heat distribution, typically operating at flow temperatures of 70–80°C. These systems are frequently paired with emitters, such as radiators or air handling units, that are sized accordingly. Retrofitting such systems to operate efficiently with low temperature heat pumps (typically 35–55°C) can require extensive and disruptive modifications, including emitter replacement, pipework upgrades and fabric improvements.
In addition, peak heat loads in non-domestic buildings – particularly in sectors such as healthcare, hospitality and industrial processes – can be substantial. Sizing a heat pump system to meet these peaks often leads to significant capital costs, space challenges and electrical infrastructure constraints. These factors mean that, in many cases, standalone heat pump solutions are not immediately practical or cost effective for existing buildings.
Hybrid systems offer flexibility and performance
Hybrid heating systems address these challenges by combining the strengths of both technologies. In a typical configuration, a heat pump is sized to meet the building’s base heating load, operating for extended periods at high efficiency. A gas-fired boiler supplements this by meeting peak demand or providing higher temperature output when required.
From a system design perspective, this approach offers several advantages:
• Optimised heat pump operation: by focusing on base load provision, the heat pump can operate at lower flow temperatures and higher coefficients of performance (COPs), maximising energy efficiency and carbon savings
• Reduced capital expenditure: a smaller heat pump requires less upfront investment and occupies less plant space, which can be a critical constraint in retrofit scenarios
• Minimal disruption: existing distribution systems and emitters can often be retained, avoiding the need for extensive internal modifications
• Operational resilience: dual heat sources provide flexibility, enhancing system reliability
Crucially, hybrid systems can be controlled to respond dynamically to external conditions, energy tariffs and carbon intensity signals. Advanced control strategies can prioritise heat pump operation when electricity is low carbon and cost effective, while switching to the boiler during peak electricity demand periods or when higher temperatures are required.
Alignment with FHBS requirements
The FHBS introduces a more stringent compliance framework for both new and existing non-domestic buildings. But it is primarily a standard for new homes and new non-domestic buildings, with only limited relevance to existing buildings undergoing certain types of refurbishment.
While there is a clear policy direction toward electrification and on-site renewables, evidenced by measures such as the default assumption of 40% solar PV coverage, there remains a need for solutions that can deliver compliance in complex real-world scenarios.
Hybrid systems can play a key role in this context. The retention of existing compliance metrics, such as the Target Emissions Rate (TER), Target Primary Energy Rate (TPER), and Fabric Energy Efficiency, means that designers retain familiar tools for demonstrating performance. Hybrid systems can be modelled to achieve favourable outcomes across these metrics by balancing electrical and gas energy inputs.
Moreover, the introduction of delivered energy as a voluntary reporting metric highlights an increasing focus on actual energy consumption. Hybrid systems, with their ability to optimise energy use across multiple sources, are well positioned to perform strongly in this regard.
Importantly, the FHBS allows for flexibility through compliance modelling trade-offs. This creates opportunities to integrate hybrid systems alongside other measures, such as solar PV and improved fabric performance, to achieve overall compliance.
Potential impact on the energy system
Beyond individual buildings, the widespread adoption of hybrid systems could deliver significant system-level benefits. By enabling faster uptake of low carbon heating technologies, hybrids can accelerate emissions reductions across the existing building stock.
As the electricity grid continues to decarbonise, the carbon intensity of heat pump operation will decrease further, enhancing the environmental performance of hybrid systems over time.
At the same time, the use of gas boilers within hybrids provides a pathway to incorporate emerging low and zero carbon gases, such as hydrogen or biomethane. This future-proofs installations and aligns with broader decarbonisation strategies for the gas network.
From an energy system perspective, hybrids can also play a role in managing peak electricity demand. By shifting load between electricity and gas, these systems can help alleviate pressure on the grid during periods of high demand, supporting overall system stability.
The FHBS places strong emphasis on the integration of on-site renewables, particularly solar PV. Hybrid systems are inherently compatible with such technologies, enabling the use of locally generated electricity to power heat pumps.
The introduction of structured compliance routes for low carbon heat networks provides further opportunities. Hybrid systems can complement heat network connections, either as part of a building-level solution or within network energy centres, offering flexibility in meeting varying load profiles.
Policy considerations and next steps
To fully realise the potential of hybrid heating systems, it is essential that policy-makers recognise their role as both an immediate and transitional solution. In particular, hybrid systems should be eligible for grants and support mechanisms, reflecting their contribution to emissions reduction and system flexibility. Compliance frameworks should accommodate hybrid configurations, ensuring that their benefits are captured in modelling methodologies.
The transition to Net Zero in non-domestic buildings will not be achieved through a single technology pathway. While electrification is central to long-term strategy, the realities of the existing building stock demand flexible, scalable and pragmatic solutions.
Hybrid heating systems offer a means to deliver immediate carbon reductions, align with emerging regulatory requirements and provide a bridge to a fully decarbonised future.
