Your contractor is correct. Section 1205 of the Uniform Building Code (1979) states that where bathrooms have natural ventilation by means of openable exterior openings (i.e., windows or skylights) with a minimum of one and a half square feet, a mechanical ventilation system or bath fan is not required.

So much for building code minimums. Now we must address your needs. Even though you have an operable window you may, in fact, need one. When there is an abundance of steam accumulating in the bedroom it is a sure sign that a fan is needed. We strongly recommend that you consider installing one.

In addition to attacking your steam problem, bathroom fans can help to remove less-than-pleasant odors associated with this area of the home.

Sorry, but there is no such thing as a noiseless exhaust fan. Some however, are less noisy than others. Fans are rated by the Cubic Feet per Minute (CFM) of air that they move, and also are rated by the level of noise they emit. The building code requires that a bath fan provide a minimum of five air changes per hour. Some simple math will tell you just what size fan you will need.