What is the diameter of duct required if the airflow is 500 CFM at a velocity of 600 FPM?

To determine the diameter of the duct required for a specific airflow rate and velocity, you can use the relationship between airflow (CFM), duct cross-sectional area, and air velocity (FPM). The basic formula connecting these variables is:

[ \text{CFM} = \text{Area} \times \text{Velocity} ]

First, calculate the cross-sectional area needed for the duct using the airflow and velocity. Rearranging the formula gives:

[ \text{Area} = \frac{\text{CFM}}{\text{Velocity}} ]

Plugging in the values:

[ \text{Area} = \frac{500 , \text{CFM}}{600 , \text{FPM}} = 0.8333 , \text{square feet} ]

Next, to find the diameter of the duct, you need to convert the area from square feet to square inches because duct diameters are typically given in inches. Since there are 144 square inches in a square foot:

[ \text{Area} = 0.8333 , \text{square feet} \times 144 , \text{square inches/square foot} \approx 120 \