I have a bathroom that is 576 cubic sq.ft. with shower/tub. There is a window in the bathroom. There is also a 70 CFM fan. We are getting way to much moisture in the bathroom after showers and we are getting mildew on the ceiling and only on the ceiling. What can we do to fix it? Is it a matter of the fan being too small for the area. It is a 70 sq.ft. room. Also, the fan is running and vented correctly. Please help. Thank you.