Using a 10 inch flexible duct with 15% compression and 700 FPM velocity, what is the approximate CFM air quantity?

To determine the approximate air quantity in CFM (Cubic Feet per Minute) for a 10-inch flexible duct with a 15% compression at a velocity of 700 FPM, you first need to calculate the effective diameter of the duct after accounting for the compression.

Starting with a 10-inch diameter, compressing the duct by 15% means the duct’s effective diameter is reduced. The calculation for the reduction is:

Effective Diameter = Original Diameter - (Compression Percentage × Original Diameter)

For a 10-inch duct:

Effective Diameter = 10 inches - (0.15 × 10 inches) = 10 inches - 1.5 inches = 8.5 inches

Next, you can calculate the area of the duct using the effective diameter. The area (A) in square feet can be found using the formula for the area of a circle, A = π(d/2)²:

1. Convert the diameter from inches to feet: 8.5 inches ÷ 12 = 0.708 feet.

2. Calculate the radius: Radius = 0.708 feet / 2 = 0.354 feet.

3. Now, use the formula for area:

A = π(