Our existing kitchen extractor fan vents to an outside wall via the flat style rigid ducting. The system works well with a decent flow of warm air routed outside.
Unfortunately, the brick vent needs to be moved as part of a conservatory installation and the installers choice is to raise the vent 6 brick courses.
My concern is that any condensation or driven rain would fall back down the ducting and onto the kitchen units. I’d prefer to route the duct down by about 3 to 4 courses to allow any condensation to escape naturally.
It will be too close to the new roof which has a bigger ring beam and box gutter. No option other than to move it up or down within the wall cavity. Luckily, there are specific duct adaptors for this purpose.
The crux is it has to move but what are the perils of going up vs down ?
When we had our conservatory built we had the same problem, but we had to raise our outlet about 15 brick courses. They used a 90 deg bend, ran rigid ducting up the wall to the conservatory roof and fitted a gravity flap like the one below on the outside with lead flashing around. It never caused a problem. I had to take it apart recently and there is no sign that water ever got in…
That’s good to know. Do you use your hood often ? Mine’s on the very exposed side of the house and the wind rips the flappy vented ones to bits unfortunately.
Did you use the attached fittings to move it within the cavity ?
Apparently, if you move it down it can lead to a back pressure because the hot air will want to rise but where it will live will be slightly better sheltered. I guess I’ll have to speak to the builder on the day.
We use the hood every day. Although the wind does catch it the flap has stayed intact for 25 years. Being at a roughly 45 deg angle rather than vertical may possibly have helped. Our outlet was a 100mm round pipe through the wall and we used a round to rectangular 90 deg ducting bend to send it up the wall, although as it turned out the cross-sectional area was too small but it worked for all that time so it can’t have been too bad.
When I was looking for the link to the flappy cover I thought I noticed a different type which may be more robust. I’ll see if I can find it again.
Thanks. I’ve had success in the past by buying a new vaned unit and soaking it in very hot water so the vanes become flexible enough to remove and then soaking them again to reposition in the old frame.