honestly, with my 400 watt (in a 2x5x5 closet) i can get away with using a 4" 170 cfm fan for ventilating my hood, and it creates enough air exchange to keep the plants happy. i think you'll be fine with one. and if you find that you dont need the other fan, you can always expand (get more lights, bigger space,) or return it. itll work out. btw, where do you order your fans from? i usually get everything from hydroponics.net