Cisno 4" Inch Duct Fan Exhaust Vent Air Cooling Hydroponic Inline Blower 100 CFM It offers an inexpensive and quiet alternative to an Inline Fan. Flange Size: 4". Sturdy plastic impeller blades. 100 CFM (Cubic Feet per Minute). Compatible with 4" Carbon Filter. Voltage: 110V / 60Hz. This duct fan is lightweight and operates as smooth as any fan we've come across.