How To Install Very Quiet 50CFM 1.2Sone Bathroom Ventilation And Exhaust Fan3inch Duct Ceili Bathroom Extractor Fan With Humidity Sensor What is CFM? CFM (Cubic Feet per Minute) measures fan air movement. Ultra Quiet 1.5 Sone Bathroom Fan with 80 CFM Power – Quickly removes moisture from bathrooms up to 85 Sq. Ft, keeping air fresh. No Attic Access Needed... CFM increases as air movement increases. Quiet bathroom fan with humidity sensor - Find the lowest price on Ventilating for bathroom up to 110 Sq., Ft TD-BF-02 90CFM0., 8Sones. A higher CFM is best for a larger bathroom; a lower CFM may be adequate for smaller spaces., TD-BF-01 110CFM1., 0Sones. About this item Very quiet bathroom fan (1.5 sones) and Strong air movement (80CFM) for bathroom up to 85 Sq. Ft 7.5in x 7.25in x 6in with 4in duct Galvanized steel Housing resists corrosion UL and HVI certified for performance assurance Mounting Opening How to choose your Bathroom Fan? What is a sone rating? Sones, or the sone rating, is a term used to describe sound levels. Higher sone ratings indicate a louder bathroom fan. Lower sone ratings are found on quieter fans.