On Mon, 17 Nov 2008 05:30:11 -0800 (PST) someone who may be
geraldthehamster wrote this:-

It would be possible to extract the lower bathroom by means of a
ceiling fan that ducts up into the eaves space, then up inside the
sloping roof, joining the same vent chimney thing Above the upper
bathroom ceiling by means of some kind of T.

It is possible. There are Y connectors which will join two runs of
ducting into one. They have a flap valve which blanks off the unused
duct if one fan is running or is in a mid position if both are
running.

Is this a good idea, or might I end up blowing wet air from one
bathroom into the other, or causing water to condense and run down the
duct into the other bathroom? Would it be better simply to put in a
second vent chimney thing lower down, in the eaves, to vent the lower
bathroom independently?

It is better to have a separate vent, provided that this vent is not
a means of letting water into the structure of the building due to
inadequate installation.

No matter which way you do it, since the ducting is vertical you
should take precautions against condensation.




--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54