Broan QTRE100S Ultra Silent Humidity Sensing Fans with Sensaire Technology 4" Ducting Size Nearly silent operation 1.5 Sones, 100 CFM Sensaire technology detects the rapid rise in humidity over time Integrated 20 minute auto shut-off timer Energy Star qualified Detects a rapid rise in humidity. Humidity is sensed at the ceiling level Shutoff timer factory set at 20 minutes Fits 2-Inch by 8-Inch ceiling construction UL listed for use over bathtubs and showers when connected to a GFCI protected branch circuit Energy star qualified, HVI certified