t joint m8 if 2 4inch say I woulf use a 6 inch fan but that's jst me so all the active carbon gets used instead off it being sucked right out even on mine turned right down when u look in the fan its black from the moister in the carbon being sucked through , I'm gonna get a carbon active blanket and use that around my cf and get active carbon 2 stick inside my duckting aswell jst 2 b sure then run it on a t joint with a jar off onna connected 2 it for the air 2 blow over if u can follow that lol