Okay, I'll do some mangled descriptions, bear with me...
I want to set the cooker hood up into the chimney (with building reg gap of 750mm between gas hob and hood). The ducting will then go out to the right (through the side wall of the chimney breast and out the external wall on the right). So, it'd be a kind of up-and-then-across shape (very technical, I know).

I'm thinking I need to find a built-in hood that will fit the space plus a ducting kit.
( crackhouseceilidhband Fuck off back to Mumsnet, Thu 15 Apr 2010, 10:50, 1 reply, 16 years ago)

Doesn't sound too complicated. Obviously the chimney isn't used for a fire.
There are quite a few hood + ducting kits available. I was just looking in the Elica catalogue for just such.
If your'e prepared to knock the holes in the flue it should be easy enough. You might find it easiest to core the wall first: that could go wrong if the chimney is built up inside at just that spot! Be prepared to knock out some bricks on the face of the chimney breast.
Assuming at least a 5" duct, you might find it helpful to use a rigid drainpipe pushed through the space to support the ducting. Or even groundwater piping.
Edit Just re-read what you had explained. You're only going out one side of the chimney! Really does sound very staightforward. Or does flexible ducting not shape up to the job? I'd imagine once you have knocked a few bricks out of the side of the flue it will look a lot simpler.
( Larry Vest One day at a time, sweet Jesus, FFS., Thu 15 Apr 2010, 11:09, Reply)

Sounds very promising. Especially since I don't have to do the building work myself.
I'm just sourcing the stuff.
( crackhouseceilidhband Fuck off back to Mumsnet, Thu 15 Apr 2010, 11:26, Reply)