... 's HIGH EFFICIENCY AND LOWER NOISE. O. BACKWARD FAN /Moterized Impeller APPLICATIONS-. HEAT RECOVERY, RANGE HOOD, AIR EXHAUST EQUIPMENT-. GENERAL VENTILATION ... OR F O. MODEL NO.-. BOB-180/30-2P ; PLASTIC IMPELLER/ 2POLE-. BOB-190/45-2P, 2S ; STEEL OR PLASTIC / 2 ... ,4 POLE-. BOB-225/50-2S,4S ; STEEL IMPELLER / 2, 4POLE-. BOB-250/50-2S,4S ; STEEL/ 2, 4POLE ...