me brought next idea :
But then you've got the situation where you go in to get the towels to wash,
open a window, kill a fly etc., and the damn thing turns on unnecessarily for
half an hour!

As you say, 20watts running for 20 minutes - so what!


It just seems to me this hasn't been thought through properly. There should
be a connection in the shower unit provided by the manufaturer which provides
power when the electric shower is turned on. It's only an extra ten or twenty
watts after all so you wouldn't need to uprate the shower cable.

If the shower in use were the only time the fan might be needed, I
agree, but for most people it is needed when the bathroom is occupied,
so an occupation switch (PIR) works better.


Anyway, reading around a bit it appears that most fans are switched from the
light switch and I'm not sure how that gets past building control when it can
obviously be left off when showering?