http://www.htgsupply.com/categories/ventilation-odor-control/fans/high-velocity-fans-blowers is where you can purchase the duct fans.
Growbright Duct Fans are high quality duct booster fans, available in 4" , 6" and 8" diameters. Growbright fans feature top quality components and precision formed and balanced fan blades constructed of polycarbonate (rather than metal blades that become easily unbalanced and corroded). Growbright In Line duct fans are often used for cooling grow tents, grow rooms and grow light reflector hoods. A Growbright Inline Duct Fan from HTGSupply - http://www.htgsupply.com - is a reliable and cost effective way to keep temperature in the indoor garden under control. Use one fan per light to increase the efficiency of an exhaust system. Also use these fans to boost airflow in long stretches of ducting.
