Usually expressed in terms of inches of water gauge (“wg)
• Static Pressure (SP):
– Pressure in the duct that tends to burst or collapse the duct
– Always measured perpendicular to air flow
– Can be negative (suction) or positive (pressure)
• Velocity Pressure (VP):
– Pressure required to accelerate the air from zero velocity to
some velocity
– Always exerted in the direction of airflow
– Always positive
• Total Pressure (TP):
– TP = SP + VP
– Can be negative or positive