Our researchers Xinyi Zhang and Richard Fitton have been featured in the CIBSE Journal for their latest work exploring how ventilation systems will perform under the upcoming Future Homes Standard (FHS), marking a significant contribution to the evolving field of low-carbon housing design.
In their article, “HEM unlocked: modelling ventilation under the Future Homes Standard,” they examine the transition to more airtight and highly insulated homes in England, set to take effect from March 2027. These changes will make mechanical ventilation systems—such as decentralised mechanical extract ventilation (dMEV) and mechanical ventilation with heat recovery (MVHR)—a necessity rather than an option in new-build housing.
They undertook testing, based using one of the zero-carbon-ready homes located in our Energy House 2.0 facility, which revealed that while SAP and HEM broadly agree under steady-state conditions, significant differences emerge when dynamic behaviour is considered. Notably, HEM predicts around 24% higher space heating demand compared to SAP, with even greater increases in electricity use due to its more detailed modelling of heating systems.
A key finding highlighted in the CIBSE Journal feature is how ventilation-related heat loss is treated differently. HEM’s ability to simulate real-time interactions between wind speed and outdoor temperatures—factors that often coincide during cold UK winters—results in higher calculated heat losses than SAP’s averaged approach. This reveals a systematic underestimation of heating demand in traditional models.
The authors also point to major advancements in how MVHR systems are represented. Unlike SAP, which relies on simplified efficiency factors, HEM incorporates detailed variables such as duct length, insulation, pressure conditions, and fan heat gains. This shift allows for a more realistic representation of system performance, though the authors note that the final compliance outcome is also heavily influenced by simplifying assumptions embedded in the FHS framework.
Despite improvements, the research identifies a shared limitation in both modelling approaches: neither fully accounts for how air and heat move between rooms, an important factor in real-world ventilation effectiveness.
The feature concludes that while HEM represents a methodological step forward—particularly for ventilation modelling—the transition introduces new complexities for designers and assessors.
This work underscores both the opportunities and challenges ahead as the UK shifts towards more sophisticated energy modelling and tighter building performance standards.