Here is a current vertical stack, with the base of a CANFAN50 pulled by a 220 CFM inline fan (out of tent). The filters are accompanied by the recommendation for CFMs... two complete room change-outs per minute is on the top side of good, and if it is replaced with fresh air, guarantees adequate CO2. (Remember to figure out a way to get air into the tent to replace the air leaving.) 220 CFM is closer to the bottom size of this can's recommendation, but matches the internal dimensions of the tent rather nicely. (That's a silly way of saying that the filter is over-sized.) I picked the filter for it's dimensions with regard to the ducting and matching where I think I want the light to hit the plants.