How to choose your Bathroom Fan? What is a sone rating? Sones, or the sone rating, is a term used to describe sound levels. Lower sone ratings are found on quieter fans. Higher sone ratings indicate a louder bathroom fan. What is CFM? CFM (Cubic Feet per Minute) measures fan air movement. CFM increases as air movement increases. A higher CFM is best for a larger bathroom; a lower CFM may be adequate for smaller spaces. TD-BF-01 110CFM1.0Sones. Ventilating for bathroom up to 110 Sq. Ft TD-BF-02 90CFM0.8Sones. Ventilating for bathroom up to 90 Sq. Ft TD-BF-03 70CFM2.0Sones. Ventilating for bathroom up to 75 Sq. Ft TD-BF-04 80CFM1.5Sones No Attic access Needed Installation,Ventilating for bathroom up to 85 Sq.FT TD-BF-04H 80CFM1.5Sones with Humidity sensor, Ventilating for bathroom up to 85 Sq.FT TD-BF-05L 70CFM2.0Sones with LED light ventilating for bathroom up to 75 Sq.FT. TD-BF-06 70CFM0.3Sones ventilating for bathroom up to 75 Sq.Ft TD-BF-07 110CFM0.8Sones with Humidity sensor ventilating up to 110 Sq.Ft TD-BF-08L 80CFM1.5Sones with LED light Ventilating for bathroom up to 85 Sq.FT TD-BF-09L 80CFM2.0Sones with LED light, Ventilating for bathroom up to 85 Sq. FT TD-BF-10 110CFM1.2Sones with No Attic access Needed Installation,Ventilating for bathroom up to 110 Sq. FT TD-BF-11 90CFM1.5Sones with Ventilating for bathroom up to 90 Sq. FT TD-BF-12L 90CFM1.5Sones with LED light Ventilating for bathroom up to 90 Sq. FT TD-BF-13 50CFM1.0Sones DC Motor with No Attic access Needed Installation,Ventilating for bathroom up to 50 Sq. TD-BF-14L 50CFM1.0Sones LED light Ventilating with No Attic access Needed Installation,Ventilating for bathroom up to 50 Sq. TD-BF-15L 110CFM1.2Sones LED light Ventilating with No Attic access Needed Installation,Ventilating for bathroom up to 110 Sq.