It's important to have proper air circulation to decrease moisture in the bathroom, especially when there are no windows. Otherwise, mold and mildew will quickly build. As it forms in cracks and other spots that are hard to reach, the difficulty in which to remove the mold will only increase. As a result, you can wind up spending hours on efforts for eradication. If you are purchasing a new fan, there are a couple of specifications which are essential to note. The CFM (cubic feet per minute) measures the flow of air. This number will need to be higher as the room size gets larger. Another factor is the sone. This is the noise level. A low number will indicate a quieter fan.