I used a 5500BTU in a 4-1/2 x 8 x 6-1/2 tent with 2 600W air cooled HIDs and its enough to keep it cool, but not dry enough. With a 70pt dehumidifier in there at least one is always running and humidity varies between 50 and 60%. (with 6 4ft tall plants and 85 outside temps.). It will keep it at 85 deg with uncooled bare bulbs (95 deg outside temps) but runs continuously. How much heat your lights put out is your biggest factor. It would be OK for maybe 800W of HID if the room is fairly airtight and the light is cooled separately.