wrote in message
The complicated part is that I would like the fan to only come on when
there's nobody in the washroom ie when the light is off.
The reason is because especially in the winter I dont want the fan on
when someone is in the room, sucking heat.

Is this possible?

Thee are plenty of timer switches that can be put in. Any electrical supply
house will have or get them for you. I don't know how your wiring is, but
you will have to separate the fan from the light if not already.

As for sucking out the heat, that is not a problem. When the shower is on,
the hot water is giving off a lot of heat as well as moisture so you really
want to start it when the shower starts. With the door closed, it will not
suck that well, but will still prevent some of the fogging up you normally
would get. IMO, leaving the door partly open works even better, no fan
needed.