Air Duct Flow Calculator

The Formula

The formula for calculating airflow rate in a duct is:

\[Flow Rate (CFM) = Velocity (fpm) \times Duct Area (sq ft)\]

Where:

• Flow Rate: The volumetric flow rate of air (in cubic feet per minute, CFM)
• Velocity: The speed of air in the duct (in feet per minute, fpm)
• Duct Area: The cross-sectional area of the duct (in square feet)

Calculation Steps

1. Calculate the duct area in square feet: Area = (Width × Height) ÷ 144
2. Multiply the air velocity by the duct area: Flow Rate = Velocity × Area

Example Calculation

Let's calculate the airflow rate for a duct with dimensions 12" × 8" and an air velocity of 1500 fpm:

1. Duct Area = (12 × 8) ÷ 144 = 0.6667 sq ft
2. Flow Rate = 1500 × 0.6667 = 1000 CFM

Visual Representation

This visual shows the airflow rate in a duct based on our example calculation.