The minimum control for a bathroom fan is a simple wall switch.
Sometimes the bathroom lights and the fan will be tied together. Now when you have a noisy fan, this can be quite tiring, so to avoid the noise you use the bathroom in the dark.The biggest problem with the simple wall switch control is that you will turn it off as you leave the bathroom, long before the humidity from that shower has left the room. The advantage is that this switch costs only $2 to $3.
What else is available?
You can buy a manual timer for around $15 to $20 . The problem with the manual timer is the tick tick tick noise as it sounds like a bomb is about to go off. Not pleasant when relaxing in the tub or doing some serious reading on the throne. It does however keep the fan going for a few minutes giving you a chance to remove most of the moisture.
Now you can get electronic timers just for this job from companies like Lutron Electronics. They are quiet and efficient, although you are probably in the $20 to $40 range.
For $20 to $60 you can get a dis-humidistat. Now we are getting serious. You can still turn the fan on manually if you want to get rid of odours, but if it is moisture, the control will turn itself on (at your desired humidity setting) and it will stay on until the humidity goes down. This could even help to dehumidify the whole house if this is the only exhaust fan you have.
Cadillac controls? You might want to look at the top of the line NuTone bathroom fan: QT100:LHM SmartSense. It is a good quality powerful but quiet fan. There is a built in dis-humidistat right in the unit. There is a night light built into the fan, that is actuated by a motion detector (no glaring lights at 3am), or a full ceiling light run by the standard wall switch. But expect to pay around $400 for the whole package.
If you want a mould free bathroom, you really do need a bathroom fan, and some way to properly control it.
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