Some reflectors have 2 connections for ducting. Sometimes 1 connection is on the side and the second one is on the top. The reason you have 2 is so you can connect a fan (or flex ductwork from a fan) to one side of the reflector and connect a second piece of flex duct to the other connection so you can duct it to another fixture or out of the room.i'm not sure what you mean, i only have one spot of my hood to hook up a fan, and its the perfect size for a 120mm fan.