MVHR Systems

Posted 7th April 2020


Ventilation is a critical element of any building design, it goes hand in hand with insulation and airtightness. We have been told countless times how people ‘like fresh air’ and don’t like these modern sealed up buildings, but our experience of surveying buildings is quite different. Many home owners and a large proportion of home renters do not open windows, they seal up the vents, and don’t use extract fans, resulting in very poor indoor air quality. If a house is draughty, then there will be greater air changes, but only when the wind is blowing, on still days it will be as poorly ventilated as a house which is sealed up.

Mechanical ventilation systems have been in use for decades and the construction industry understands that whole house ventilation can reduce energy consumption and improve air quality. Unfortunately the design and installation of these systems is often terrible. It seems especially prevalent in design and build and developer-led projects, as it is seen as an area where cost savings can be made.

We recently inspected two social housing units with MVHR, neither were working properly despite being annually serviced by a contractor. The first mistake we found was that the units were located in an unheated loft with no access for changing or cleaning filters. Further errors included using flexible pipes which had collapsed preventing any air flow; roof tile vents designed for small extract fans with totally inadequate apertures; poor routing of ducts; no summer bypass; no kitchen filtration; and placing the intake vent on a dark south facing roof slope which acted like a solar panel- drawing hot air into the system in summer.

As a result the properties were badly under-ventilated and severely overheating. We arranged for a local contractor to strip out the units and prepare for the installation of new wall mounted units in the kitchen. Our local specialist then installed and commissioned new systems with built in cooker hoods. We will monitor and see what difference these make to internal comfort over the next 12 months.