In article ,
Harry Bloomfield writes:
on 13/05/2018, me supposed :
And as the regs require this ventilation when the shower is in use surely
there's no point operating the extractor from a light switch because then it
doesn't have to be used.

Fit a PIR operated fan. That would cover the bath, or shower, or toilet
being used in a room. Mine includes both a built in PIR and a humidity
sensor. It comes on if you walk in the door and it continues to run
after the bath or shower has been used, until the excess moisture has
been dispelled to the outdoors.

I did a shower room for someone else. For that, the fan is on a
run-on timer with the light as usual, but to get a longer run after
a shower, it's also triggered by a pipe stat on the shower hot feed,
so it will stay on until the pipe cools. That part of pipe has an
8mm parallel pipe which snakes up behind the bathroom mirror, so
that when you use the shower, the mirror is heated. When the shower
is finished, this loop up behind the mirror convects via the piece
of pipe with the pipe stat on it, to cool that pipe down.

When I get around to it, I will write this up with diagrams.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]