Extraction for cooker hood

I am replacing an existing cooker hood with a new model. The new hood has 150mm ducting supplied, the old one was 125mm.

Because of the design of the new hood, I cannot just enlarge the existing outlet hole as the new hood sits higher and a new vent will be needed further up the wall.

Two questions :-

What is the quickest/easiest way to knock through the new vent hole? I do not have any 'specialist' equipment just a hammer drill, chisels etc.

Secondly how do I fill in the old exit hole? The outside is easy enough I guess - will just remove bricks around the hole and replace with new whole bricks, but what about inside? the cooker hood chimney will cover the old hole so can i just fill the hole with something like expanded metal and plaster over it?

grateful for any advice.

To make the new hole...either hire a core drill of the appropriate size - complete with drill - or chain drill loads of holes around a marked circle of the correct diameter, plus clearance and knock it out with a hammer and cold chisel.
To fill the outer old hole - jam some pieces of broken brick into the aperture and render over with sand and cement if the finish doesn't matter...if it does then you can either chase out for new bricks or simply leave the old grille in place - its up to you. The same goes for the inside really, but use cement or plaster.
John

Assuming you have a cavity wall, try not to drop rubbish down the cavity.

First of all, I'd stitch drill around the hole on the inside, then join up the dots and create the hole with the chisel.
Then drill through to the outside to orientate yourself to the outside and repeat the process. Try to not create too large a hole on the outside. The vent cover will hide a little bit of over-exuberance, but not much.

Once the duct is in place, wedge it on the inside with pieces of wood to stabilise it and then fill in around the edges on the outside with mortar.
When that's set (watch the weather or it could freeze) you can fill in around on the inside with an expanding foam.

You could also use the expanding foam to fill the old hole on the inside. You could fill partly with the broken bricks also. This can be trimmed with a knife or similar once set. Try not to put so much foam in that it breeches the cavity. Alternatively just use the old broken bricks mortar'd in place on the inside skin, then plastered to finish.

Thanks for the helpful replies gentlemen,

The new cooker hood has a 150mm vent pipe, I seem to be struggling to find anyone who stocks gravity flap vents to fit that size of ducting.

I have a couple online but wondered if anyone knew if any of the DIY outlets or Builders Merchants chains carry them? (tried Wickes & Jewson but no luck)

Thanks

Look at Toolstation 82914....in stainless
John