CFM is the acronym for Cubic Feet per Minute — the measure of air volume moved by the fan blower. Choose a fan with a CFM rating appropriate for your room size to ensure adequate ventilation.
What does 80 CFM mean?
A fan's ability to move air is measured in cubic feet per minute (CFM). The bigger your bathroom, the higher the CFM rating you'll need. A fan should have a CFM rating high enough to replace the air in your bathroom at a rate 8 times per hour. Most fans are rated from 50 to 110 CFM.
How do Sones work?
Sones are a linear measurement, like inches. Doubling the sone value is equivalent to doubling the loudness (i.e. one to two, two to four is doubling the sound level twice). Your 4-sone fan will be more than four times a noisy as a 0.9 sone fan. Always look for a quiet fan, or it will not be used.