How to Calculate the Air Flow & the Static Pressure Drop Through the Grill

Air flows continuously through a system's vents.
••• Jupiterimages/ Images

Building owners must monitor the flow through air duct grills to test how well their ventilation systems work. A pilot tube assembly, a device containing multiple probes, measures the static pressure drop between the grill’s two sides. The air flow rate through the grill is proportional to this pressure and is related to the grill’s size. If these values turn out far less than you expect them to be, this implies a fault in your system such as an unexpected break in a conduit.

    Hold the pilot tube assembly’s static pressure probe at a right angle to the air flow.

    Hold the assembly’s total pressure probe parallel to the air flow.

    Read the assembly’s pressure gauge, which states the static pressure drop across the grill in inches of water.

    Find the square root of the static pressure. For example, if the pressure drop is 1.3 inches of water: √1.3 = 1.14.

    Multiply this answer by the grill’s area, measured in square feet. For example, if the grill measures 2.2 square feet in area: 1.14 × 2.2 = 2.5.

    Multiply the result by 4,005, a conversion constant: 2.5 × 4,005 = 10,012, or just over 10,000. This is the air flow through the grill, measured in cubic feet per minute.

Related Articles

How to Calculate the Flow Rate of a Commercial Fire...
How to Calculate Fan Output
How to Convert PSI to PSIG
How to Calculate Evaporator Sizing
How to Convert CV to GPM
How to Calculate GPM From Differential Pressure
How to Calculate the Horsepower of a Compressor
How to Calculate Static Head
How to Size Gravity Drainage Piping
How to Calculate Flow Rate With Pipe Size and Pressure
How to Figure GPM Water Flow on an Existing Chiller
How to Calculate the Flow Rate of a Commercial Fire...
How to Calculate GPM from PSI for Water
How to Convert HVAC Tons to Amps
How to Convert an MPA to KN
How to Find Relative Barometric Pressure
How to Calculate the Square Meters in a Triangle
How to Calculate Potential Difference
How to Convert Steam Flow to Megawatts
How to Calculate the Velocity of Water Through Pipes