roof fan, high qualty and low price, life long, good apperance and easy for maintainence. roof fan, high qualty and low price, oemGRAD brandapplied to indoor ventilating, supply air and other gas of non-spontaneous combustion, non-explosive, non-volatile, harmless, non-corrosive. Impurities property of the gas: no stickum, or dust/rigid particle content no higher than 150mg/m, temperature no ...