Coolair belt-driven upblast power roof exhaust fans are designed to discharge vertically so that air velocity seals the opening against rain and snow while the unit is in operation. When the fan is switched off, counterbalanced dampers close by gravity to provide a weather-resistant closure. The fiberglass dampers close quietly and serve as a skylight when unit is not in operation. The JBH is a low profile upblast fan noted for lower initial cost, proven reliability and efficient operation for commercial and industrial applications. They are designed for use in situations where it is practical for the motor and drive components to be recessed into the roof curb.