Should an MVHR Exhaust vent into a cavity wall or directly outside?

[Doran]

Hi all,

We recently discovered that our MVHR system vents into a cavity wall, with the air then escaping through an airbrick on the exterior.
We’re wondering if this setup is correct or if it could be contributing to a damp issue we’ve been struggling with.

Background:

• We moved into our 10-year-old flat just over two years ago and have had an occasional damp spot in our bedroom, in a corner by an external wall (the wall has the airbrick)
• Engineers have been investigating for some time, including water tests and cavity wall inspections, but the cause remains unclear.
• The issue occurs year-round.

What we’ve recently noticed:

• The MVHR exhaust blows directly into the cavity wall, which then vents through an airbrick.
• There’s presently significant condensation on the cowl (which we recently added to try and reduce water ingress).

Questions:

• Is this a normal setup for an MVHR exhaust?
• Could this be contributing to our ongoing damp problem?
• could condensation build up and cause this (but then this shouldnt be the case in summer would it?)

Here’s a video showing the airbrick and cavity wall.
And a photo of the airbrick (now with the recently added cowl).

Would really appreciate any insights!

 

[polesapart]

No, of course it should not vent into the cavity.

Any fule kno that.

 

[Doran]

Well, in that case, apparently not the builders of our property

 

[Roddy Young]

You only mention the exhaust. Both exhaust and intake should be on the same wall or roof about 2 metres apart. This prevents wind blowing into one without being "balanced" by the other.

 

[Doran]

Hmm, another failure then. There is no intake on that wall at all.