How to replace a kitchen hood duct

[redhexagonal]

My 350m3/h cooker hood is 4.5m from the exterior wall, and is currently connected to an exterior vent with 100mm aluminium ducting inside a bulkhead. I'd like to have better extraction, 500m3/h or more, and it seems like I need 150mm duct for higher powered hoods. Unfortuately the floor has been glued and screwed down over the bulkhead now, so I was thinking maybe I could connect the 150mm duct to the old 100mm duct and drag it through the bulkhead? It might be tricky because there is quite a bit of insulation in the bulkhead now, and additional timbers to level the floor mean the duct has to bend around a timber as it exits. Then I would need to core a bigger hole in the exterior wall - is it possible to cement up the old hole in the cavity wall and core a hole about 10cm to the right, so the duct doesn't have a kink at the end, or would that weaken the wall? Any other ideas?

I would go straight out behind the hood, but there are timbers, pipes and a waterproof membrane that make it complicated...

 

[BlueLoo]

Core a bigger hole (8") and feed in solid 6" plastic pipe from the outside.

This will be a much more hygiene friendly solution than using coiled duct and pipe is stiff so getting it back to the cooker hood will be much easier.

Wouldn't worry about the hole in the wall, easy enough to reinstate behind a vent.

 

[redhexagonal]

Core a bigger hole (8") and feed in solid 6" plastic pipe from the outside.

This will be a much more hygiene friendly solution than using coiled duct and pipe is stiff so getting it back to the cooker hood will be much easier.

Wouldn't worry about the hole in the wall, easy enough to reinstate behind a vent.

Thanks. Where can I get 5m of rigid 6” duct? I can only find lengths up to about 2m

 

[BlueLoo]

Thanks. Where can I get 5m of rigid 6” duct? I can only find lengths up to about 2m

6" wavin soil pipe.
Available from most builders providers.
It can be joined by a coupling easily enough.

It is a favourite trick of builders everywhere who need to add ventilation ducting to a build.