Ian Atkinson wrote:
Lobster wrote:
wrote:

If it was me, I'd then pass a length of ducting through the wall eg:
http://www.screwfix.com/app/sfd/cat/...31554&id=54391
Needs to be angled slightly outwards to help any rain/condensation drain
out.

Fit that flush with the outside wall and mortar in place and make good,
when it's set, add a vent like:
http://www.screwfix.com/app/sfd/cat/...31691&id=20389
This fits snugly into the ducting.

Chop off the ducting on the inside wall leaving an inch protruding, then
connect that to the exit of the extractor fan using flexible hosing.

That's a great help David, thank you!

I'll order the bits and then I think I'm all set to go

Be aware that there are different diameters of ducting/hosing available
- check the diameter of the spigot of your extractor fan, and then buy
kit to match... you can get adapters etc but obviously easiest not to.

Also - check whether or not the hood has a built-in flaps to close hole
off when not in use; if not it can get pretty draughty when you don't
want it to: this can be avoided by fitting a vent on the outside wall
which incorporates flaps (not as effective as the built-in ones, but
probably better than nothing)

David