INDUSTRY COMMENT: NIBE
Rethinking retrofit: why heating alone isn’t enough
If retrofit is the UK’s biggest decarbonisation challenge, then how we specify systems will play a defining role in its success
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cross the HVAC industry, there has been significant progress in shifting heating away from fossil fuels. Heat pumps are now firmly established in the conversation, supported
by policy, funding and growing installer confidence. But in many retrofit projects, the focus remains narrowly defined: replace the heat source, improve efficiency, reduce carbon. When retrofit strategies focus solely on heating system replacement, this underlying issue remains unresolved. In some cases, it can even be exacerbated. Improvements to insulation and airtightness, while essential for energy performance, can further restrict natural ventilation pathways.
The limits of a single technology approach
Air source heat pumps (ASHPs) have become the default solution for many retrofit scenarios, and rightly so in the appropriate context. They offer a proven route to low carbon heating and are well understood across the supply chain. However, they are not without limitations. External space requirements, planning constraints and acoustic considerations can restrict deployment, particularly in flats, dense urban housing, or properties with limited outdoor access. More fundamentally, ASHPs address one part of the building system - heating and hot water - but do not resolve issues relating to ventilation or indoor air quality. In properties already experiencing condensation, damp or stale air, this can leave a critical part of the problem untouched.
Towards a whole-home approach
In practical terms, this means considering heating, ventilation and hot water as interconnected elements rather than separate systems. For specifiers, it opens up a different set of design questions:
• How is air moving through the building?
• Where is moisture being generated and removed?
• Can energy be recovered as part of that process?
• And how can these functions be integrated into a coherent system?
This is where exhaust air heat pumps (EAHPs) are starting to re-enter the retrofit conversation.
Reframing EAHPs for retrofit
Historically, EAHPs have been closely associated with new build applications. The reason is largely practical. Traditional systems are physically
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large, with ducting required to return to a single central unit. Retrofitting this into an existing home, particularly one with finished interiors, can be disruptive, complex and costly. As a result, EAHPs have often been discounted early in retrofit design. What is now changing is the way these systems can be configured. By separating the air handling function from the hot water unit, a split approach allows each component to be located where it makes the most sense within the property. The air handling unit can be positioned in a loft or cupboard, while the hot water cylinder remains in a familiar utility space. Instead of large duct runs converging on a single point, ventilation can be routed more flexibly within a defined zone, with only small-diameter hydraulic connections linking the two elements. This does not remove the need for ducting and it does not make every property suitable, but it does broaden the range of homes where an EAHP-based solution becomes viable.
Implications for retrofit design and delivery
For specifiers and installers, this shift is less about a new product and more about a different category of retrofit. Rather than simply replacing a boiler with a heat pump, the system can deliver continuous, controlled ventilation, heat recovery from extracted air, low carbon space heating and domestic hot water production within a single, integrated approach. From a building performance perspective, this addresses several challenges simultaneously.
Moisture is actively managed, reducing the risk of condensation and associated fabric issues. Indoor air quality is improved through consistent airflow rather than intermittent extract. In addition, recovered heat contributes to the overall efficiency of the system.
A realistic view
It is important to be clear that this is not a universal solution. Properties with extremely limited ducting routes, unsuitable loft conditions or already effective ventilation strategies may still be better served by alternative approaches. In many cases, ASHPs will remain the most straightforward and appropriate option. The point is not to replace one default with another but to expand the available toolkit.
A question of specification
As retrofit activity continues to scale, the industry faces a critical choice. It can continue to apply single-technology solutions across a highly varied housing stock or it can adopt a more nuanced, system-led approach.
For specifiers, this means moving beyond the question of “what replaces the boiler?” and towards a more fundamental consideration of how the home performs in terms of heat, air and overall comfort. EAHPs, particularly in more flexible configurations, are one example of how that thinking is evolving. Not as a replacement for existing technologies but as part of a broader shift towards integrated retrofit solutions.
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18/3/26 10:27 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2026 17
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