ventilation help 4 or 6 "

hi all in the middle of my second setup and don't know if ill need a 4 or 6 inch I line fan can someone help?my space is rougly 2' wide X 3' long X 5' high
wooden box inside of a closet
400 watt air cooled hps . The ballast is outside the box
my intake will be a hole cut in the wall with around 2.5 foot of ducting connecting it to the box with bends to trap light I would like to put some sort of intake filter on since we smoke cigs and want fresh clean air in the box (suggestions on a filter?)
the exhaust will be 2.5 - 3ft worth of ducting to the ceiling with a carbon filter (not sure if ill go DIY or bought)

the room the closet is in stays around 70 degrees

I want to go with sunleaves wind tunnel inline fan just for the exhaust I'm just not sure if I should use a 4 or 6 inch
I would like to keep the noise to a minimum so would it be better to use a 4 inch and maybe need a booster intake fan if necessary or a 6 inch with passive intakes ?

thanks for the help

Hi there, if you are going to use the fan for both the cool tube and filter, then go with the 6 inch. The best way to do it IMO is Filter > Fan > Ducting > Cooltube > Ducting out of the box and if possible outside the room the box is in.

I use a 4 inch fan in a 1mx1mx2m tent, but that's just for he filter and then I run a separate 6 inch fan to the cooltube. In time, im just going to replace them out for a 200mm fan.

in that area, i think u could use a 4 inch inline, at 180 cfm,that will replace all the air in ur box in minutes.

thanks for the replies anyone with a similar setup that can help?