@Tester101 Welcome to the party! That's my way of offering many thanks for your help. That answer is awesome! As it turns out, our bathroom is small enough for 110 cfm, but Mike (contractor) said never go below 150, just doesn't think it's worth it. I thought we must need to have some moisture - I was already cold enough when the old fan was working, and it left the same amount of moisture. I take very long, hot showers - hubby's are shorter and colder, so there's less moisture after.

He thought there should be none, but Mike disagreed.

Part of our fear was because the whole problem happened when the back wall of the shower fell apart and opened to reveal lots of black mold. The shower was tiled in 1972 when the house was built, and when we bought it a few years ago it looked fine. According to Mike, there had been "grout failure" for years, we just couldn't see it.

Our new fan is a Panasonic Whisper Ceiling Fan with sones of 0.3 so it's very quiet! I thank you again, and will try to stop being paranoid!!! Mike was very clear to leave the fan on for 20 minutes after, so I appreciate that confirmation. You're very awesome and I thank you again!