Ruth MacEachern of EnviroVent explains why mechanical ventilation with heat recovery systems are the key to improving energy efficiency in modern homes.

Housebuilders are building to ever more stringent Building Regulations requirements for airtightness, however to ensure an energy efficient home with a good level of indoor air quality, mechanical ventilation with heat recovery is essential.

Mechanical Heat Recovery Ventilation (MVHR) is effective in extracting excess moisture in the air to prevent humidity build-up and condensation in wet rooms like bathrooms and kitchens, yet by also recovering the heat from the outgoing stale air, it reduces the energy demands of the home.

Heat Recovery & Energy Saving

MVHR systems can be the answer to making an airtight home energy efficient, whilst achieving high levels of indoor air quality.

These systems are designed to recover the heat from the outgoing air and transfer it to the incoming fresh air. This heat exchange process means MVHR systems can significantly reduce the energy required to heat or cool the incoming air, resulting in lower energy consumption and reduced carbon emissions. Heat recovery systems can typically recover about 73-95% of the heat in exhaust air – they can also significantly improve the energy efficiency of buildings.

Overheating can be mitigated with the summer bypass function measuring indoor and outdoor temperatures and adjusts the ventilation speed accordingly. However, it is important to firstly consider the main fabric of the building, orientation and shading to avert any potential overheating issues.

While mechanical ventilation systems offer numerous benefits, their integration in airtight homes comes with its own set of challenges. Maintaining the integrity of the building envelope is crucial as any unintended air leakage can compromise the performance of the mechanical ventilation system. 

Typically in newly constructed buildings, duct leakage can range from 25-40% (Source: Department of Energy Report), which is unacceptable for high-performance buildings such as Passivhaus designs. To address this challenge, it is essential to ensure correct sealing of ductwork, which should minimise leakage to less than 3% of the system’s air volume. This requires a combination of effective design, quality installation and rigorous testing to achieve optimal airtightness.

Insulation and seals should be inspected to ensure they are intact and there are no gaps or leaks that could compromise the airtightness inherent to the Passivhaus concept. Carrying out regular checks and maintenance is particularly important with Passivhaus ventilation systems.

Building the homes of the future

For housebuilders, the integration of MVHR supports the requirement to build homes that are not only compliant with current standards but are future-proofed to address the evolving requirements, such as the Future Homes and Building Standard (FHBS). The latest Building Regulations require that all new build homes need to be future-proofed with low carbon heating and world-leading levels of energy efficiency. They set out the ambitious target of a 30% reduction in carbon emissions for new dwellings as an interim target, up to the introduction of the Future Homes and Building Standard in 2025. 

Achieving this requires a comprehensive approach that extends beyond traditional insulation methods. As this standard sets a higher benchmark for energy efficiency, incorporating highly efficient MVHR systems has become essential.

As technology advances, it further strengthens the position of MVHR systems as an indispensable component of energy-efficient homes. Smart ventilation controls can also provide greater control to the user and ease of commissioning for the installer. Innovations in MVHR continue to enhance precision, automation and monitoring, which not only improves the user experience but also contributes to optimised energy usage.

When it comes to MVHR, the design of the system is crucial to the overall efficiency of the building. If a ventilation unit is undersized, it could lead to the under performance of the system, with an air flow rate that is too low, which can result in high humidity levels in dwellings. It can also mean a unit has to work extra hard in an attempt to achieve airflow rates, resulting in excessive noise and increased energy usage. This is why manufacturers work closely with specifiers from the design stage to ensure that new homes can meet the requirements for both ventilation and air tightness.

Passivhaus – meeting the standard

As the Government has strict limits to meet on carbon emissions, housebuilding requirements are set to become even more stringent. 

The Passivhaus concept is being adopted by many social housing providers and some developers because it sets a benchmark for achieving energy efficiency through ventilation and heat recovery.

Passivhaus, obviously, presents another dimension in the need for energy-efficient ventilation systems. Achieving Passivhaus certification requires meticulous attention to detail in terms of insulation, airtightness, ventilation and overall energy performance. MVHR fits into this framework, providing a comprehensive solution that addresses the requirements of Passivhaus construction. Ventilation systems must be certified to meet the Passivhaus standard to be part of a Passivhaus build.

Long term benefits

The advantages of MVHR extend beyond compliance. Housebuilders with a long-term vision recognise the value of incorporating MVHR as standard in their projects. It can be seen as a strategic investment that enhances the marketability of homes, positioning them as forward-thinking by offering eco-friendly dwellings that meet the growing demand for sustainable living spaces. MVHR can also lead to long term benefits for homeowners such as lower energy bills, and can potentially lead to an increase in property value.

So MVHR becomes a compelling choice on the road to zero carbon. The combined benefits of energy efficiency, good quality indoor air quality and compliance with building regulations, means MVHR systems are future-proofed to meet the demands of today and tomorrow.

Integrating mechanical ventilation systems in airtight homes, including Passivhaus buildings, presents both challenges and opportunities for the new build market. Effective MVHR system design can go a long way to address the potential challenges posed by airtightness.

With the benefit of ventilation systems with heat recovery, airtight buildings can enjoy high levels of indoor air quality, energy efficiency and reduced carbon emissions over the lifetime of the dwelling. 

Ruth MacEachern is product manager at EnviroVent