Fan Size mm / inches Fan Speed RPM Motor (HP) Air Delivery CFM 300 (12) 1440 0.25 600-2000 400 (16) 1440 0.5 2000-2600 400 (16) 1440 0.75 2600-4000 450 (18â??) 2880 1 4000-6000 600 (24) 1440 1 6000-8000 700 (28) 1440 2 8000-9000 800 (32) 960 1.5 9000-11000 800 (32) 960 2 11000-14000 900 (36) 960 3 14000-19500 1000 (40) 960 5 19500-26500