Fitting new kitchen extractor duct

[kamoshika]

Apologies if this is in the wrong forum - didn't seem to fit any of the others.

Our kitchen currently has an extractor hood that just recirculates the air, and doesn't do that very well. I'm looking to replace it with a new one that will extract to outside, but obviously to do that I need to fit a duct through the wall. Fortunately there is a very conveniently located air brick just above a cabinet on the wall next to the hob, that has been plastered over on the inside, and was sealed on the outside when we had cavity wall insulation installed.

What I'm planning to do is:

Break through the plaster on the inside
Take out the airbrick on the outside (it's already loose, so not going to be difficult!)
Fit a ring of cavity wall brush (the stuff they use to stop the insulation spreading to next door in a semi-detached house) to keep the insulation back.
Fit a duct through the wall with appropriate vent on the outside wall, and fill the gaps around it with mortar.

Couple of questions:

Does that sound like a sensible plan, or is there a better way of tackling it?

Does anyone know where I can get a short length of the cavity wall brush? I've tried googling but haven't found anything useful (if you google cavity and brush most of the results are to do with teeth!)

Thanks in advance for any advice you can offer

 

[foxhole]

The duct will hold back the insulation so no need for the brush.
Your current extractor hood could be reused, most are made dual purpose, i.e recirculate or extract.

 

[kamoshika]

Thanks for the speedy reply. I did wonder whether I really need the brush. I guess I was mainly thinking it would make it easier to deal with fitting the duct, especially if I need to enlarge / reshape the hole through the wall, if I didn't also have insulation spilling out.

To be honest the old extractor hood is so old and manky I'd rather buy a new one that try to deal with cleaning the current one up. It looks like it was fitted by the previous owners when they had the kitchen done in the 90s sometime, and I'm not sure it's been cleaned since!