Not sure if help is still needed, but I have a 40x40x140 piece and simply use two powerful modern PC fans. Extraction is at 2000 RPM/60 CFM and intake is at 1000 RPM/40 CFM. It works pretty well, but you can only get two plants in there if you plant in 7 liter or 5 liter pots. 5 liter will work...