Advice please for kitchen extractor installed badly

20 Apr 2018
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United Kingdom
Hello all,

I'd love to hear people's thoughts please on the kitchen extraction we have going on in our house.

We're a typical red brick victorian terrace. 4 years ago our builder built us a nice new kitchen, installing a false ceiling with spotlights etc. They also installed a flue hose from the cooker hood, up into the new ceiling void, through it over the width of the kitchen and terminating on the internal surface of a large (10" square?) original exterior air brick which was originally below the level of the original ceiling, but which is now fully enclosed within the new ceiling void.

Now I presumed they'd used some kind of coupling to mate the flue hose to the air brick, creating an air-tight seal. However a couple of years ago while working under the floorboards of the 1st floor (while the kitchen extractor was running) I noticed a haze coming up under the floorboard. Of course it was some kind of leak / blowback from the extractor flue. From feeling around the exterior of the air brick while the extractor is running I can feel that only about one quarter (bottom right) of its area is blowing, so the flue is clearly just resting against the internal surface of the air brick and not connected in any sensible way. Perhaps it's even sunk down from the position the builders left it in. I'm not sure what % of the flue air flow is actually escaping the house, but it's certainly not 100%.

We spoke to the builder about this ages ago - (we were planning to redecorate our bathroom at the time and lifting the bathroom floor should provide relatively easy access to the flue and air brick, although it might be necessary to break through the original kitchen ceiling if it's still present in that area) - and he said he'd sort it no probs. Fine.

Life being what it is we never got on with the bathroom, so we never did anything about the flue.

Now I'm back on the case, and wondering:

- Was this just a bad job from the start? Should anyone ever terminate a kitchen flue at an airbrick without mating it?
- Does a flue->air brick mating gizmo exist?
- If not, what's the correct solution? Some kind of plastic air vent system which would be mortared into the wall instead of the air brick?
- What's the danger of oil / cooking residues from building up in the void? If it's anything like our cooker hood then grease does build up, probably a fire risk and potentially horrible job to clean?

Advice gratefully received!
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Was the route taken with the flue the shortest way or is there a wall closer that he could have used?
There may well be fatty/oily deposits inside the ducting but, on their own, they probably won't cause a fire risk. However, and it's a big HOWEVER, if there should be a fire in any of the rooms the ducting passes through whilst in the ceiling void, then there is an increased risk that the fire may spread further more quickly if the ducting ignites.

It should not have been left propped against an airbrick but fed through the external wall and terminated correctly to a flanged plate, preferably with hinged louvre vents to prevent blow back of external air.
As this was done a number of years ago I doubt the builder will be interested in fixing it unless you agree a price with him.
No it shouldnt terminate on the inside.

The extraction ducting should connect to a through wall kit, which has a rigid plastic tube. Externally there should be a grill with drop down flaps to prevent wind and rain getting in
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