What size hole for a 150mm kitchen extract duct?

I’m fitting a new cooker hood which uses a 150mm duct. I’m using flexible aluminium ducting.

I’m struggling to work out what size hole to drill in the outside wall (victoriain brick approx. 250mm thick).

152mm? Drill rental seem much cheaper and I could squish the ducting a bit to get it in (it deforms very easily).

162mm? Not many local rental places even do them. Overkill?

I’d buy a straight bit of tube for the bit through the wall. Its only a few quid from screwfix or toolstation. Should be fine with a 152mm hole.

Also core drilling old brick can be a pig of a job. Might be easier to stitch it.

Just about to do this myself. Albeit 127mm hole for 125mm ducting from what I’ve read.

Now I’ve bought the core drill (Ebay) I keep hearing that stiching may be easier 🙁

6″

Put ducting in freezer 1st so it contracts, then fit it

I’ve also been advised to drill a pilot hole all the way through the wall in the centre to start. That can then be used as a guide if part drilling from the inside and part drilling from the outside.

It’s a 3m length. I may struggle to get it in with the frozen peas..

Sounds like a 152mm hole will be fine.

Mmm to stitch or to core drill…

Low density block – core drill, Victorian bricks – stitch

152mm drill a pilot hole with a metre drill bit normally a 10mm for the core bit pilot to sit inside while you start the core off. When core bit started (approx 5-6mm in the brick take out the pilot from the centre of the core bit and carry on.

Slow and steady dont force weight onto the core bit as its ment to do its own work. Stop every so often to clear out debris fror a smoother and quicker cut.

Use either a “dry” bit or a “wet” bit. If your even contemplating stiching that size you need to re evaluate what your doing.. Stiching is rough as toast and using the hammer function on a sds you will loosen all the bricks around where your drilling and make a right mess. Core bit with a extension bar and a standalone core drill with a clutch… Dont even think of using a sds on rotary….. Snapped wrist ahoy.

Hire a core bit and drill from a local hire shop will cut through like butter they will normally havev hilti drill a dd100 and a norton core bit both make life easier.

If you haven’t already bought everything i’d step the ductwork down to 125mm – 150mm is overkill for domestic cooker hood extraction.
I did this on my current installation with no problems – Screwfix/Toolstation sell the step down adaptors.

A 125mm hole is easier to core out than a 152mm hole.

If you hire a core make sure you don’t push on it too hard. Otherwise it will turn into a VERY expensive hole. You are literally holding it agains the wall and letting the core do the work. We used to make a fortune off renting out core drills due to damage even though we would show people how to use them. The other favourite was people using it in a hammer drill then bringing it back because after about 10mm it stopped working.

I did a pilot hole before employing the core bit.

If you hire a core make sure you don’t push on it too hard.

Good advice. It was my Dads and he insisted on doing most of the 40 odd minute cut and haranging me the whole time I took a turn about this 😀

I used one of these types of square section vent kits which fits through a brick sized aperture and has a round fitting to the flexible hose: http://www.amazon.co.uk/Spares2go-Universal-Cooker-External-Kitchen/dp/B00QV5DYLA

You will require an adapter for larger 150mm hose: http://www.i-sells.co.uk/megaduct-220-straight-round-to-rectangular-adapter

I drilled around the mortar surrounding a brick with a standard percussion drill and long masonry bit, using bolster and standard chisels to assist and worked through to the other side. Carefully filled any gaps between square plastic duct and brickwork with some expanding foam, masking edges off with duct tape to control any foam expansion overflow. The foam when set also nicely seated the plastic duct pipe in the wall.

The ducting is visible so any step-down / adaptors is going to look unsightly.
I’ll rent a quality 152mm core drill on Monday and take my time drilling.
Thanks all.

FFS, Do I have to spoon feed you everything….Take the peas out!

Don’t stitch drill that’s just bodge! Core every time. Try and keep level if anything you are better running up slightly from outside to in. The pilot hole is only to start the core. Once it’s cutting it will merrily go on its way. Determine whether they are wet or dry cut cores and some can use hammer.
Fwiw my job today is fitting 11 grills over cooker hood ducts.

For added entertainment value, we did a 152mm hole from outside into our in use and fully decorated kitchen, to minimise dust i put a large biscuit tin over the pilot hole in the kitchen and gaffer taped the hoover to it as extraction, & had the wife hold it in place whilst i drilled, it worked, and saved us a grey dusty mess. Make sure you hire a drill with a clutch!!!

qwerty – great idea.

Also means I need to buy more biscuits.

Pilot can be drilled from inside for exact hole location (hold Hoover tube immediately below bit to extract) and then cut from outside. Travis Perkins trestles are £2 per week to hire, add 3 scaffold boards and you then have a decent working platform. You want the drill at hip height, think Arnie and big **** off machine gun.

I hired a 150mm core drill to do this with a big drill. I would recommend also hiring the drill as it should have a clutch that will slip when the bit gets stuck (it will). I couldn’t believe how physical it was. Pilot hole yes. Also drill from outside to inside as there is a lot of dust. The 150mm bit wasn’t wide enough for the duct, there was a lot, an awful lot of swearing. Managed to bodge it in the end. Didn’t help that I cut through the oven and hob supply…. Add £200 for sparks to rewire this… Not my finest hour.

Had our plumbers do ours for a recent new kitchen.

Glad I did now as they hit a brick tie!

I did this once and without thinking put a downward angle from outside in. Every time it rained it ran through the pipe. .. had to cut it out and redo.

Therefore I would take wrightysons advice.

Thanks. Cat tax;

Thanks for the core drill advice re: clutches, got a similar problem with the added complication that I’m enlarging a hole.

162mm is what I read for 150mm, 2mm really isn’t enough give for outside diameter. Most hire places seem to have a 162mm option, I’m gonna go for it just to make life infinitely easier.

Is there any way you can use rigid duct? Will cost a bit more but will be quieter, work better and look better (if visible)