Tried and true tools for the heating and cooling trade, wisely adapted for cooling HID lights. An Inline Duct Fan is a reliable and cost effective way to keep temperature in the indoor garden under control. Works with standard sheet metal or flexible duct work. Use one fan per light or to increase the efficiency of an existing exhaust system. Larger sizes available. This high-efficiency fan will cool lamps and provide air movement through filters. The four-inch, 30-watt In-Line Duct Fan pushes 65 cfm and comes with a pre-wired power cord.