Cooker Hood Ducting

dw14

Hi all,

Got a new 60cm cooker hood which seems quite powerful at 558 ㎥/h max extraction rate.
Model is: Samsung.nk24m5070cs
The install instructions say ducting should be 150mm or 6" but the existing hole in the double brick kitchen wall is smaller.
The length of run is about 2 metres from top of hood to outside wall grille with one 90 degree bend.
Spoken to Samsung and got two different answers. One said it must be 150mm or it wouldn't work right and other said it could be reduced to 125mm. There's a reducer in the box.

Should it be ok to reduce to 125mm at top of extractor and run that to grille or have 150mm to the wall and reduce for the last 300mm through the double brick wall?

Thanks

DaftyDuck

Run as wide as possible to the wall, especially if there are any turns. Use the reducer as late in the run as possible.

Any constriction will slightly reduce flow, as would long pipe runs, or multiple turns. However, at a guess, you'll be fine doing this!

dw14

Ok, thanks DaftyDuck, my thoughts too.
If I have to reduce from 150 to 100mm due to the hole being smaller than 125, would that be too big a drop in size maybe?

DaftyDuck

Who can tell? Best you can do is try it out. It may put a little more strain on the motor, it may not be quite as effective, but it should still work. However, the cross sectional area of 100mm is much less than half that of 150mm, and the surface area for resistance is proportionally higher.

Bigger hole the better. But, if needs must...

thescouselander

I had the same issue and installed the reducer at the cooker hood end - works fine for our setup.

martinthebandit

Just a thought, but increasing the size of the hole would be an easy, simple and (probably) more practical option.

dw14

I thought about widening the hole as the best option but not sure how to do it ��

martinthebandit

dw14 wrote: »

I thought about widening the hole as the best option but not sure how to do it ��

Mark where the edges of the enlarged hole will be. Drill lots of small holes as close together as possible along the marked lines then, using a bolster chisel and a lump hammer, join the holes up.

Well that’s how I would do it.

FreeBear

martinthebandit wrote: »

using a bolster chisel and a lump hammer, join the holes up.

A bolster would be way too big for this job - I'd suggest a scutch chisel...


Others would probably say "use an SDS drill with a chisel attachment", bit not everyone has an SDS drill.

There is another way - Make a plug out of a thick lump of wood and insert it in the existing hole. Mark the centre, drill a 12mm hole through and then use a 150mm core drill (you can hire diamond core drills fairly cheaply).

martinthebandit

Ah but I haven’t got a scutch chisel but I do have a bolster chisel.

dw14

Ok, I might get a scutch chisel then

Would a very long drill bit help to drill & chisel, drill & chisel and so on until through the hole or just drill to start then chip away?
Take a bit of time to do I expect?