Bathroom ventilation in one form or
another is not only desirable, it is also
required by building codes. Although
its main purposes are to provide a
healthful exchange of air and remove
odors, ventilation also helps in controlling
excessive humidity.
Thus, in a residential bathroom with
no window that opens to the outside,
you need a ducted electric fan to meet
code requirements.
The problem here is that a fan will
only remove stale air and moisture
when it is turned on, and a window will
only do the job when it is opened. Both
are at the mercy of the occupants.
Of course, moisture removal from a
bathroom can be accomplished simply
by leaving the bathroom door