BIB12MIL 12 Whirlybird

12in Whirlybird Turbine Vent Mill. Easy installation, reduces energy bills, reduces winter ice build up. Internally braced all aluminum turbine ventilator. Permanently lubricated upper and lower ball bearings that ensure long life and no maintenance. Riveted at every connection. 21 air-foil curved vanes with rolled vane edges to deflect water. Exclusive vari-pitch base adjusts to 12/12 roof pitch. Large flashing for easy installation. Tested to withstand winds of 147 m.p.h. These are exhaust vents and require proper intake to create a balanced ventilation system. {BIB12MIL}