Ducting size/hole size for 120mm cooker hood outlet spigot?

[john738]

As part of my ongoing kitchen renovation I just ordered an integrated cooker hood, which has a 120mm diameter output spigot.

Looking online for a 120mm ducting kit there only seem to be very limited options, I found these two:

1) https://www.manrose.co.uk/product/43077-cooker-hood-venting-kit-120mm-5inch/ (however they call it 5 inch, which is not really 120mm, but rather 125mm... Aso in the technical specs it says: "Hole sizes: 140mm hole for the 125mm kit.")

2) https://www.appliancesdirect.co.uk/p/eiqventkit125cowl/electriq-eiqventkit125cowl-ducting (this is actually 125mm but it says the following in the details: "electriQ hoods are sold with a plastic hose and a 125mm to 120mm adaptor. This kit includes a premium aluminium flexi hose, which provides a more permanent solution alongside the outdoor flap grille and fixings provided."

Any suggestions on what to go for?

Also, I need to make the hole in the kitchen wall as there isn't one, and option 1 for example says it needs to be a 140mm hole. Looking at core drill bits that doesn't seem to be a standard bit size either, 152mm seems more common. Can I drill a 152mm hole and maybe cement the gap?

Thanks

 

[JohnD]

The bigger hole will enable you to fit a bigger duct if you ever want to and will accommodate any inaccuracy. Tilt it slightly so any water runs outward.

You can stuff round the duct with mineral wool to fill the gap and block draughts. Mice will not eat it and it is not flammable. You can use expanding foam but you will never be able to move it after. In a cavity wall, use mineral wool to form a collar in the cavity.

You only need to mortar round the ends of the pipe to hold it firm and resist weather. I poke it in with my fingers. You might be able to get half an inch or an inch depth. The outside is more important as it must resist weather and not crack or fall out.

 

[john738]

The bigger hole will enable you to fit a bigger duct if you ever want to and will accommodate any inaccuracy. Tilt it slightly so any water runs outward.

You can stuff round the duct with mineral wool to fill the gap and block draughts. Mice will not eat it and it is not flammable. You can use expanding foam but you will never be able to move it after. In a cavity wall, use mineral wool to form a collar in the cavity.

You only need to mortar round the ends of the pipe to hold it firm and resist weather. I poke it in with my fingers. You might be able to get half an inch or an inch depth. The outside is more important as it must resist weather and not crack or fall out.

Got it about the bigger hole, I know what to do now, thanks.
As to the ducting kit, do you reckon I should go for option 2, given that it should come with a125mm to 120mm adaptor for the hood's side?

 

[JohnD]

AFAIK 125mm is now normal for hoods.

I've done mine with all rigid PVC duct (tube, elbow, adaptors)

No flexy which IMO is tacky

I dislike the type of vent shown by Manrose, with the little flaps that rattle annoyingly in the wind until they break off (which does not take long)

I use cowl vents

Forgot to say, make the hole as high as you can. You may later want to upgrade to a canopy or cabinet, which needs a higher vent

 

[john738]

AFAIK 125mm is now normal for hoods.

This is the one I got (it is actually a cabinet integrated one - I'll drill the hole as high as possible):

Amazon.co.uk

It says 120mm diameter in the picture showing the dimensions. I'm worried I may end up with air escaping through the 5mm gap at the spigot/duct junction.

Would this adaptor do the trick maybe? https://www.tlc-direct.co.uk/Products/FD515C.html

No flexy which IMO is tacky

I use cowl vents

Thanks for the tips - I'll use rigid PVC duct and a cowl vent then

 

[JohnD]

I got my ducting from some fan supplier, there is a wide range of fittings, don't remember their name. I expect there is an adaptor to fit.

 

[john738]

I got my ducting from some fan supplier, there is a wide range of fittings, don't remember their name. I expect there is an adaptor to fit.

Found a few - thanks so much for all your help!