My 106 year old, vinyl over wood covered house has a 2nd floor bathroom. The BR has plaster walls and ceilings. There is a room above and below the bathroom. The bathroom does have an exterior wall with a newer window.

I am getting a mold problem from shower use. ARe there wall mounted ventilation fans that will not let cold air in when the fan is off?

I have never cut a hole in plaster, but I will gladly try (with a little advise). There is a light fixture on the outside wall so I could get electric to a fan.

Are there window mounted fans for this purpose which would keep me from cutting hole in the wall?