An Inline Duct Fan is a reliable and cost effective way to keep temperatures in the indoor garden under control. Available in five models. All work with standard sheet metal or flexible duct work. Use one fan per light for air cooling or to increase the efficiency of an existing exhaust system. These fans have a low static pressure which means that the longer the ducting, the less effective they will be. For longer runs, a blower is much more effective. The four-inch, 30-watt In-Line Duct Fan pushes 65 cfm and comes with a pre-wired power cord.