nick wrote:
Hi
I'm hoping somebody might be able to give me some advice on picking
and siting a suitable bathroom extractor fan.
(It seems to be a subject that few people know much about)

The bathroom has a volume of 21 cubic metres.
I'd go for the wall mounted option
In my opinion the ceiling fans with ducting, unless they are the centrifugal
type, are not very good.
They will work but take a long time to extract.
The other problem is, if they are mounted on a plasterboard ceiling, the
vibration can be quite noisy.

Another important consideration is that the fan must be appropriate for the
zone of the bathroom it is in.
What you can put in each zone is regulated
In the shower area ( and probably above the bath) is the most rigourous
zone.
For these areas you would need a proper low voltage model which aren't cheap