Cooker hood ducting - Update

[M85]

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

 

[JohnD]

a lot of older hoods had a 100mm duct. It is wearisome to core out a bigger hole, you have to fix a brace across the old one so the pilot drill will centre, and it is dusty and noisy.

I'd use the big duct and elbows, right up to the entry to your wall duct, and reduce it there. It will be noiser than if you used full-size duct, and flow will be reduced, but I expect it will still be better than your old one..

 

[M85]

a lot of older hoods had a 100mm duct. It is wearisome to core out a bigger hole, you have to fix a brace across the old one so the pilot drill will centre, and it is dusty and noisy.

I'd use the big duct and elbows, right up to the entry to your wall duct, and reduce it there. It will be noiser than if you used full-size duct, and flow will be reduced, but I expect it will still be better than your old one..

Yes, the old hood had a 100mm flexihose but I might be able to get 125mm hose through the double brick.
The hole starts at just over 125mm but could narrow slightly. 150 to 125 for the last 300mm shouldn't be as bad maybe?
What about drilling holes and chiselling? That would take ages though wouldn't it?

Never thought about the size of ducting before I bough this powerful hood

 

[JohnD]

the usual method is to hire a core drill from a tool hire shop (they are expensive to buy). If you get one you will enjoy it so much that you will drill holes for your bathroom, WC and kitchen extractors, and for a vented tumbledrier in case you should buy one in future. I did.

You could pay a plumber, it might take him an hour.

Chiselling out is hard work, and does not make such a neat hole. It's very easy to slip a piece of duct through a good hole and mortar it in. If you have cavity walls, stuff something in the gap so you can pick out dust and fragments.

 

[M85]

Ok, thanks.
Half the kitchen is installed already, will this be very messy?
An hour of a plumbers time would be well worth it to do it properly though.

 

[M85]

Looking at round to rectangle ducting as it goes up from hood into a cupboard then out to the wall.
Rectangle ducting would be better in the cupboard.
Would making a new air brick hole for a vent be an easier option and close existing hole?

 

[JohnD]

it's not difficult to enlarge a cored hole, but the person doing it has to screw a piece of wood over one or both sides of the hole to keep the drill steady. If he tries to do it freehand it will wobble, because the centre will have nothing to fit into.

the vid isn't quite how I'd do it, but you get the idea.

 

[foxhole]

Use rigid plastic or foil hose as plastic hose melts with the temp which are involved.

 

[Nige F]

Would making a new air brick hole for a vent be an easier option and close existing hole?

You'd best ask the manufacturers again - the airbrick - even a plastic one - may be too restrictive. As to enlarging the hole by 50mm I would stitch drill and chisel - less mess, lumps of brick not masses of fine dust- the stitching can be accompanied by hoovering under each hole, and a good sharp cold chisel + lump hammer will sort it. Mind you you'll never get a modern plumber to do it - needs to be old skool like me

 

[M85]

You'd best ask the manufacturers again - the airbrick - even a plastic one - may be too restrictive. As to enlarging the hole by 50mm I would stitch drill and chisel - less mess, lumps of brick not masses of fine dust- the stitching can be accompanied by hoovering under each hole, and a good sharp cold chisel + lump hammer will sort it. Mind you you'll never get a modern plumber to do it - needs to be old skool like me

Cheers. Asking a couple of general trade companies to see if they can do it at this time of year. If not, I'll drill and chisel myself
You're so right, asked a plumber and they defo didn't want to know

 

[M85]

Update

Got a local core drilling company coming on Monday to widen hole.
£80 all in.

Many thanks to everyone for your help

 

[JohnD]

Bravo!

Go for 150mm for maximum efficiency and least noise. If you haven't already got it, buy enough duct, and I recommend a cowl vent, which keeps the weather out and does not rattle annoyingly or fall apart like the multiple-flap type. You'll need a couple of yoghurt-pots full of sand and cement to mortar the duct in. Slope it slightly down to the outside so any condensation drips out.

https://www.tlc-direct.co.uk/Main_Index/Ventilation_Index/Ducting_2/index.html

http://www.fantronix.com/acatalog/6--150mm--Cowled-Vent-Wind-Baffle-Grille.html

 

[Nige F]

Update

Got a local core drilling company coming on Monday to widen hole.
£80 all in.

Many thanks to everyone for your help

That sounds pretty good

 

[M85]

Bravo!

Go for 150mm for maximum efficiency and least noise. If you haven't already got it, buy enough duct, and I recommend a cowl vent, which keeps the weather out and does not rattle annoyingly or fall apart like the multiple-flap type. You'll need a couple of yoghurt-pots full of sand and cement to mortar the duct in. Slope it slightly down to the outside so any condensation drips out.
]

Duct purchased with a bit extra just in case.

The hole will be a tight fit with the pipe. Not sure if the core cutters will do any mortaring, i'll need to ask them.
If not, is it a case of some mortar round the pipe on the outside wall to seal, then the vent put on once mortar is set?
Never touched mortar in my life, yikes!

Cheers

 

[JohnD]

Is it a cavity wall?