In-line model has removable access panel and no insulation Quiet automatic backdraft dampers Two impact-resistant centrifugal blower wheels Can be ducted horizontally or vertically Use Broan Electronic Variable Speed Control to adjust blower speed and sound level (available separately)Amperage: 2.9 CFM: 681 Collection: LoSone Duct Size: 4-1 2 x 18-1 2 Finish: Galvanized Steel Function: Utility Fan Heater Included: No Housing Depth: 11-3 4 Housing Length: 21-1 2 Housing Width: 12-1 4 Humidity Sensing: No Installation Type: In-Line Light Included: No Motion Sensing: No Sones: 3.7 UL Listed: Yes Voltage: 120 Wattage: 313 Weight: 34.00