I have a bathroom with no window, but there is a duct of about 4
metres which goes through a bedroom (boxed in at top corner of room)
and out the back.

The old fan was a cheapy axial thing which I'm sure didn't even blow
the air all the way out of the duct.

I went an bought a greenwood airvac S90 fan a while ago which isnt yet
fitted but I dont think this has an overrun or humidistat.

I'm happy to get another one as I really need a decent fan to combat
the mould which grows on the ceiling, anyone got any recommendations?
The duct is 100mm diameter.

Cheers