Blower Wheel Type Backward-Inclined Drive Type Belt Drive Includes Drive Package Yes Assembly Unassembled Wheel Diameter 36 1/2 in Airflow @ 0.250 in SP 21 120 cfm Airflow @ 0.500 in SP 20 614 cfm Airflow @ 0.750 in SP 20 108 cfm Airflow @ 1.000 in SP 19 599 cfm Airflow @ 1.250 in SP Not Applicable Airflow @ 1.500 in SP 18 557 cfm Airflow @ 2.000 in SP 17 457 cfm Airflow @ 2.500 in SP 16 258 cfm Airflow @ 3.000 in SP 14 881 cfm Airflow @ 3.500 in SP Not Applicable