Mechanical ventilation with heat recovery

Also see:

8.3.3Building integration

MVHR systems shall ensure compatibility with other building elements and not adversely affect the performance of the building. Issues to be taken into account include:

  1. weathertightness
  2. fixing of fan units
  3. firestopping.


Proprietary roof terminals should be used to ensure the weathertightness of the roof covering.

Fixing of fan units

MVHR fan units should only be fixed to parts of the building capable of taking the load. Where MVHR fan units are supported by framed structures, additional components such as noggings may be required to provide a secure fixing point.

Fan units should be located, orientated and fixed in accordance with the design, using the clips, brackets and fixings recommended by the manufacturer.


The MVHR system should not adversely affect the fire performance of the building. Issues to be taken into account include:

  • ensuring that the fire requirements of the building are in accordance with relevant building regulations
  • suitable detailing of components passing through other elements of the building
  • location and type of firestops to be used
  • integrity of protected stairs and halls
  • integrity of walls and floors.

Proprietary fire components should be suitably tested, and specified to take account of the test conditions.

Relevant standards include:

BS 476‘Fire tests on building materials and structures.’
BS EN 1365-2‘Fire resistance tests for loadbearing elements. Floors and roofs.’
BS EN 1366-3‘Fire resistance tests for service installations. Penetration seals.’