What to consider when combining the efficiency of heat pumps with the proven track record of traditional gas boilers in commercial refurbishment projects
By Jason Allen, Commercial Product Manager
The construction and operation of commercial buildings account for around 38% of global carbon emissions. Transitioning to heat pumps is therefore essential in the effort to decarbonise and achieve Net Zero. However, retrofitting heat pumps—especially in older or larger commercial buildings—presents challenges. This article explores key design considerations for installing heat pumps and how hybrid systems offer a practical first step toward decarbonisation.
Maximising system performance
Designing a heat pump system begins with reducing heat demand. An energy audit should identify heat loss areas that can be improved through insulation, sealing leaks, and optimising current systems. Lowering demand enhances system efficiency and reduces operating costs. This understanding is also vital for selecting the right heat pump size and ensuring it meets client expectations.
Once demand and expectations are clear, the next step is to choose the appropriate technology, whether a standalone heat pump, a cascade system, or a hybrid solution.
Understanding a hybrid heat pump system
Hybrid systems are becoming increasingly popular for their ability to combine energy-efficient heat pumps with reliable traditional heating, such as condensing gas boilers. In these systems, the heat pump is the primary source of heat, managing most of the load. The boiler functions as a secondary source, activating during periods of peak demand.
Heat pumps work by transferring, rather than generating, heat typically from the air, ground, or water. This makes them far more efficient than fossil fuel-burning systems. However, their efficiency drops in low temperatures (below ~4°C), often struggling to meet heating demands alone in winter.
The boiler compensates during these times, ensuring sufficient heating. When temperatures rise, the system automatically reverts to the heat pump. Because the boiler only activates, when necessary, the hybrid model maintains comfort without excessive energy use.
Cascading wall-hung condensing boilers like the Stratton Mk3, or modular floor-standing boilers like the Modumax Mk3, are ideal for hybrids. Their higher modulation prevents unnecessary fuel consumption common with large, single boilers. These boilers integrate well with commercial air source heat pumps such as the Tyneham.
Another effective configuration is dedicating heat pumps to radiator systems while gas boilers remain responsible for domestic hot water (DHW). In this setup, both operate independently but simultaneously. This avoids the need for high-temperature generation from the heat pump, allowing stable, efficient operation at lower temperatures. It also reduces the required heat pump size, pipework, and thermal storage, offering significant cost savings, especially for projects with tight budgets.
When to choose a hybrid system
Condensing gas boilers are known for their ability to quickly heat large spaces, but air-source heat pumps offer a more efficient, low-carbon alternative, which is crucial for building owners focused on sustainability. However, not all buildings are suited to standalone heat pump systems.
Older or larger buildings often have high heating demands, operate at high temperatures, and lack proper insulation. These factors can limit the effectiveness of heat pumps on their own.
In such cases, a hybrid heat pump system, incorporating new or existing gas boilers alongside air source heat pumps (ASHPs), offers a viable alternative. This approach balances performance, sustainability, and cost.
Hybrid heating in action
Stansfield Business Centre in Sunderland is a great example. As part of the council’s energy reduction initiative, they installed a 32kW Tyneham air source monobloc heat pump with a 500L buffer cylinder, alongside a Stratton Mk3 wall-hung condensing
boiler. This low-carbon hybrid system delivers reliable heating year-round with reduced running costs.
Easy to integrate
A major benefit of hybrid systems in older buildings is that they often require minimal modifications to existing setups. This makes them cost-effective, particularly when replacing failed boilers. Hybrid systems are also adaptable to changing building sizes and demands, making them ideal for settings like schools or care homes where disruption must be minimal.
Conclusion
Hybrid heating systems bridge the gap between traditional fossil fuel systems and low-carbon heat pumps, enabling decarbonisation at a more affordable cost.
That said, heat pumps carry higher capital costs than gas boilers. Despite their efficiency, high UK electricity prices mean running costs aren’t necessarily lower than gas. These financial barriers may push some building owners to opt for another gas system, albeit a more efficient one like the Modumax Mk3 fully modulating condensing boiler.
Still, hybrid systems can reduce carbon emissions by up to 80%, which is a compelling figure for businesses striving to meet environmental goals. Meanwhile, modern condensing boilers themselves offer efficiencies of up to 90%, maintaining their relevance, especially amid government uncertainty over banning gas boilers by 2035.
Ultimately, hybrid systems break down many of the barriers to adopting low or no-carbon heating technologies. However, understanding the end goal—whether to retrofit or replace—and carefully considering practical installation and running costs is essential when planning any upgrade or hybrid system design.
