The fan and cooling system depends on the size of your stealth grow box, and the type of light that you are using. Computer fans (80mm), one intake, one exhaust will suffice if you are using a smaller box. But, one of the main factors when choosing fans is the type of light that is in use. Many HPS and HID lights require an actual cooling system, because the heat that they put off will burn the plants if the air is not cooled. You want your interior temperature to be about 3-5 degrees above the ambient temperature, at the max. Hope this helps... :thumbsup: