Fans can operate in different ways so that they are suitable for the type of room and its use.

A standard fan turns on and off when switched.  A timed fan will come on when switched then run on for a set period when switched off.
A humidity fan works the same way as a timed fan but will run on until the humidity has dropped to a set level.

Standard fans are a great economic option and allow the user to decide how long the fans run.  Timed fans work well if you don't want to have to remember to turn the fan off.  Humidity fans are the best at extracting all the hot moist air from your bathroom and are recommended by the building regulations for bathrooms.

There are a lot of choices.  If you want peace of mind, that you are safe from the risks of black mold, give Chris a call for some free advice on 01332 410240