Venting Kitchen Extractor Fan

[lizard89769]

Hi,

I have a small kitchen where there is an existing extractor fan, but the air is pumped back into the room rather than being taken outside. I want ducting attached to it and a hole made in the exterior wall so the air can be taken outside.

How dirty does the ducting get inside / how often do they need to be cleaned? I could route the duct through the ceiling cavity or just attach it around the wall to the exterior wall / vent hole. If I opt for the wall then it might be easier to clean / replace but routing through the ceiling would probably mean it looks nicer..

Also, should I have a one way flap on the outside ? There are two central heating out vents near the place I want to vent out to outside, so I really don't want any air blowing in ; I often smell gas near these outlets. However, I have heard these one way flaps can make a noise when they open/close which might be annoying.

Finally, it would be nice if air could exit out of this vent passively, i.e without the extractor fan being switched on so the air in the kitchen is periodically being replaced - is this likely ?

 

[Burnerman]

Dust and dirt build up is not an issue in this situation, I find.....the air is filtered before being expelled to the outside, after all.
You should have a flap on the outside - a louvre one is fine. Without this, air can blow back in, through the extractor filter which can give an unpleasant pong.
Its unlikely that louvre vents flapping would be any cause for discomfort.
There will be minimal air exchange without the extractor being switched on.
John