PHAM NEWS | MARCH 2026 Ventilation & Heat Recovery


Closing the gap between design and performance


The technology exists to ensure that no UK home should suff er from damp and mould issues, yet the evidence suggests that poor installation and commissioning, coupled with a lack of regular maintenance, mean that too often ventilation systems are underperforming – Chris Knights from BSRIA explains more.


T


o coincide with evolving regulations, mechanical ventilation with heat recovery (MVHR) is


becoming standard in both new build and retrofi t projects. A welcome addition, of course, but with this wider adoption, we’re witnessing a worrying pattern emerging. The evidence from our fi eld


assessments is showing us that, while the technology is capable of delivering effi cient heat recovery for decades, too many systems are failing prematurely. Not because the technology is fl awed, but because fundamental installation and maintenance principles are being overlooked. Poor specifi cation,


inadequate maintenance and installation shortcuts are creating a performance gap that leads to fabric damage, tenant complaints, spiralling remediation costs and even risks to occupant health.


Cutting corners There’s no denying that the pressure to deliver housing at pace is immense. But cutting corners on ventilation is a false economy that will come back to haunt everyone involved. Every MVHR installation should


begin with a comprehensive assessment that ensures a system is designed based on fact, not assumption. This means we must assess whole building performance – rather than individual measures – to avoid unintended consequences. Building fabric, occupancy patterns, internal heat gains and local air quality all infl uence system selection. For example, a unit specifi ed for a family home won’t perform adequately in a house of multiple occupation where moisture loads and pollutant generation are signifi cantly higher. To ensure robust specifi cation, building assessments demand:


Realistic occupancy modelling:


We should no longer design for theoretical occupants. Social housing providers consistently report that actual occupancy exceeds design assumptions, sometimes substantially. This means system sizing must refl ect real-world use, including cooking patterns, drying laundry indoors and extended time spent at home. Adequate ductwork sizing: We


31


building fabric. When MVHR systems fail or are switched off by frustrated occupants, moisture has nowhere to go. Within months, you’ll see condensation, mould growth and timber decay in roof spaces and concealed voids. This is where inadequate ventilation moves from inconvenience to serious fi nancial liability. BSRIA’s testing work has


documented excessive relative humidity levels in properties with failed ventilation, creating ideal conditions for mould proliferation. The English Housing Survey 2022 reported that 4% of homes in England have damp problems, with condensation and mould being signifi cant contributors. Much of this is preventable through adequate ventilation. The sequence is depressingly


Chris Knights Business manager applied engineering at BSRIA


 Access panels should be in easy reach so that fi lters can be easily located and replaced


...properties with functioning MVHR systems maintain substantially lower relative humidity levels compared to naturally ventilated equivalents


see countless installations where undersized ductwork creates excessive system resistance. The result? Higher fan speeds, increased noise, reduced effi ciency and accelerated component wear. It’s critical to follow manufacturers’ guidance rigorously and never compromise on duct diameter to ease installation.


Accessible maintenance:


This shouldn’t need stating, but systems where fi lters can only be reached through amateur gymnastics will inevitably be neglected. Locate units and access panels where routine maintenance can be performed safely and effi ciently. Housing providers consistently report that accessibility directly correlates with maintenance compliance.


BSRIA GUIDANCE ON DAMP AND MOULD RISKS


BSRIA has recently launched a new technical guide designed to support social housing providers, private landlords and construction professionals in managing and eliminating damp and mould. The publication, BG 90/2026 ‘Dealing with Mould in Social Housing’, has been developed in collaboration with the UK Centre for Moisture in Buildings (UKCMB). It highlights the importance of addressing moisture risk alongside insulation and fabric improvements using evidence- based strategies to help providers meet heightened regulatory expectations while safeguarding tenant health and reducing long-term maintenance costs. The guide includes detailed case studies demonstrating how coordinated, evidence-led approaches can help to deliver practical results. ◼ phamnews.co.uk/326/51


Regular maintenance Bluntly speaking, if we’re not establishing clear maintenance schedules from handover, we’re setting up systems for premature failure. Research from the Zero


Carbon Hub’s ‘Closing the Gap Between Design and As Built Performance’ project found that actual building energy performance can vary from design predictions by a factor of three, largely due to installation quality and maintenance issues. To combat this, eff ective maintenance schedules must rigorously document fi lter inspection intervals, heat exchanger cleaning protocols, fan unit performance verifi cation and ductwork contamination checks, as well as system recommissioning following any building modifi cations. The economics are


straightforward. Regular fi lter changes cost a fraction of component replacement. According to the Ventilation and Indoor Air Quality Guide (CIBSE Guide B, 2016), inadequate maintenance results in reduced airfl ow that signifi cantly increases fan energy consumption, causes dramatic drops in heat exchanger effi ciency, and triggers occupant complaints. This can lead to premature component failure and potential fabric damage, requiring the system itself to be replaced, as well as other remedial works.


Serious costs The real cost of poor ventilation? Poor ventilation doesn’t just aff ect comfort: it damages the


predictable. Firstly, the system fails or is disabled due to noise/ perceived energy waste. Then, moisture accumulates in fabric over 6-18 months before visible mould appears, triggering tenant complaints. Emergency remediation begins, but underlying ventilation issues often remain unaddressed, and the cycle repeats itself. The Building Research


Establishment’s work on indoor environmental quality consistently demonstrates that properties with functioning MVHR systems maintain substantially lower relative humidity levels compared to naturally ventilated equivalents. That’s not marginal – it’s the diff erence between a building that maintains its value and one that deteriorates rapidly.


Moving forward Achieving decarbonisation targets in residential buildings depends entirely on ventilation systems that deliver consistent performance year after year. Not systems that look good at handover. This requires a fundamental


shift in how we approach ventilation. We must stop treating it as a compliance checkbox and start treating it as critical building infrastructure that demands the same rigour we apply to heating, drainage or electrical systems. For specifi ers and installers,


that means refusing to compromise on specifi cation, insisting on adequate commissioning time and providing comprehensive handover documentation. For housing providers, it means investing in predictive maintenance regimes and using performance monitoring to identify problems before they escalate. The technology works. The


question is whether we’re willing to do what’s necessary to make it work in practice. ◼ phamnews.co.uk/326/52


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40