In message , at
19:04:29 on Sun, 8 Mar 2015, Michael Chare
remarked:
The pipe from my hood runs above a couple of cupboards before going out
through a wall.

That's right - just run a duct from the output of the hood to wherever
the hole [already] is.

The fan in the hood comes on automatically whenever my induction hob is
used.

Mine's entirely manual.
--
Roland Perry