The V-Series fans are powered by an external rotor motor with a mixed-flow impeller. A mixed-flow impeller design is a cross between vane axial and centrifugal fans allowing a higher static pressure (more air volume) than any other comparable impeller design of the same wheel diameter. The housing of the V-Series is made of heavy duty galvanized steel painted with hammertone epoxy baked finish with sound dampening and a rust preventing qualities. Furthermore the V-Series fans operate between 1500 and 1700 RPM and are 100% speed controllable, making them the quietest fans on the market. V-Series fans are available in 10 configurations, from 12 to 24 inches with a range greater than 2000 CFM and up to over 7000 CFM. 3 years warranty.