In message , Jan Wysocki
writes
In article , Pete wrote:
While floors still up.....
Our "undreground" bathroom has very little ventilation only a small
opening window on the outside wall next to the extractor fan.

When the fan is on and the door closed there is no through draught to
allow fan to draw out moist air.
I have been toying with the idea of running some "squashed"
ventilation/extractor vent pipe stuff from the outside wall to the
diagonally opposte corner to the extractor fan thus allowing fresh drier
air to enter the bathroom and creating a decent air flow.

Or would it be better just to put a vent in the bathroom door to allow
interior "warmer" air to flush through to the fan?

Even better would be a heat recovery ventilator which uses a
countercurrent heat exchanger to heat the incoming air with the
outgoing exhaust. That way you'll spend less energy on heating and
you'll reduce draughts. However, these devices are an order of
magnitude more expensive than simple extractor fans.

Which is of course the problem.

I considered one of these when I did my bathroom, but it just didn't
seem worthwhile (on this scale - whole house ones make more sense) any
energy savings will be small, certainly not cost effective, and the
volume of air drawn by the extractor isn't really enough to create a
significant draught (there are plenty of other routes for draughts....)

I would probably just put in vent if necessary in the bathroom door and
draw air through the house - as long as there is ventilation of some
sort into the house.

I found no need for this, even with the door closed the vent seems to
work ok - there is a gap under the door, and anyway. it's rare that the
door is fully closed when not in use .


--
Chris French, Leeds