Currently I run 4" Vortex 190cfm exhaust fan for my 4'x2'x5' tent and it does a good job I'll say that, but the thing has to run pretty hard, making it fairly loud and not descrete at all. I have a carbon filter in my tent, 4' of ducting, then my fan is actually mounted outside my tent on the closet wall where its pushing out the filtered air through ducting in the ceiling. I'm looking for an option that's SILENT or nearly silent that would keep my room cool. I know most fans are 6" and such but I've already ran ducting and all that for the 4" so maybe I can just get 6" fan and run a reducer to 4".