Calculate air velocity in feet per minute from CFM and duct size, and convert rectangular duct to equivalent round diameter using the ASHRAE formula.
Velocity tells you how fast air moves through the duct. High velocity can mean noise and higher pressure drop; low velocity in a long run can mean poor throw at the outlets. The equivalent round diameter gives the round duct with the same friction and airflow as a rectangular duct, not the same area.
Estimates based on your inputs. Always verify against the manufacturer's data and the codes that apply where you work.
Describe the symptom and your readings. Brixon helps you work through the free, quick checks first, then the deeper tests. It can be wrong, so confirm on the equipment.
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