On Sunday, June 30, 2019 at 11:01:37 AM UTC+1, wrote:
On Sunday, 30 June 2019 09:41:32 UTC+1, Jeff Layman wrote:
On 30/06/19 09:18, newshound wrote:
On 30/06/2019 09:04, Stephen wrote:
Hello,

My hob has a cooker hood above it but it has been installed in
re-circulation mode. If I change the carbon filter it might absorb
smells but it will not do anything about steam, so I would like to
convert it to extract outside. That would be straightforward: the hood
is about 6.5' or 2m ish from the wall. I could run ducting along the
top of the cupboard units.

What ducting is best: circular or rectangular? I know the oblong one
can be hidden behind a pelmet but I'm happy to have unsightly circular
if that is better - does one shape offer less resistance to the air?

the big difference is between smooth walled & corrugated flexible, The latter is bad news for airflow, especially with axial fans which only deliver low pressure.

The thing that may be a problem is that the wall is only 2' wide. Then
there is a french door in the wall and I'm not sure whether there is a
lintel above it.

I'm just wondering whether I can cut a 6" hole in the wall for the
extractor fan if the wall is only 2' wide; that's a quarter of the
width of the wall, which sounds a lot.

OTOH I live in a semi, so although I only have 2' on my side, there is
another 2' on my neighbours side which mirrors mine.

What do you all think?

Thanks.

6" in 4' should not be a problem

Modern house presumably? Cavity wall with insulation?

The OP needs to watch out if the cavity wall insulation is old
polystyrene beads which no longer stick to each other. When the hole
saw is removed the stuff will just pour out (especially if it's a
standard two-storey house and the hole is at the top of the ground
floor). I would advise him to have a vacuum cleaner ready and to shove
the ducting in a soon as possible after the hole saw is pulled out.

Drill an 8mm test hole. You can block that trivially easily if it rains beads.


NT

Yes. Flexible hose kills the efficiensy of the air flow handling . Also get the largest size recommended by the extractor manufacturer. SWMBO got a Miele fan and it could cope with 6" pipe. I used smooth wall plastic pipe. It works perfectly. Even frying fish laves no residual odours in the kiytchen and no steam at all