New research has highlighted concerns over MVHR (mechanical ventilation with heat recovery), showing the need for clarity across the industry

Neil Jefferson

You may recall the Zero Carbon Hub鈥檚 work on ventilation and indoor air quality (VIAQ) in airtight new homes. Supported with research from the NHBC Foundation, it focused on the ventilation system known as MVHR (mechanical ventilation with heat recovery) and highlighted a string of concerns in relation to design, installation, commissioning, operation and maintenance.

Given that there are 24,000 MVHR installations annually, these issues must be addressed, and I am pleased that we have taken a further step towards this with this month鈥檚 publication of new NHBC standards guidance specifically addressing the issues associated with MVHR.

Indoor air quality is at the top of my list of concerns in airtight, zero-carbon homes

Drawing breath at the conclusion of the work on MVHR, we have begun to ask ourselves whether attention should now turn to other types of ventilation installed in new homes. At many points during the MVHR work, questions have been raised about the effectiveness of passive stack ventilation and continuous mechanical extraction - both systems that share some common features with MVHR, such as air valves, long runs of ductwork and exhaust terminals. Given that, why should these systems escape the problems we have found with MVHR?

But what about background ventilators and intermittent extract fans (aka trickle vents and cooker hood and bathroom fan) - the most common of the four Approved Document F ventilation systems?

Reassuringly, it is simple to understand and use. But there is anecdotal evidence suggesting that even this most simple of systems is not used properly. The trickle vents left open or closed, dependent on the weather on moving-in day; cooker hoods not used because you can鈥檛 hear the telly; and, let鈥檚 be honest, who ever cleans the filter?

As I have said previously, indoor air quality is at the top of my list of concerns in airtight, zero-carbon homes and we must have confidence that all types of ventilation are delivering safe and healthy indoor environments. With the next edition of Approved Document L about to hit the shelves, am I alone in wondering whether there should have been parallel review of Approved Document F to resolve these concerns?

Neil Jefferson is director of the NHBC and chief executive of the Zero Carbon Hub

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