If a return register measures 20" x 30" and has a velocity of 500 FPM, what is the capacity in CFM?

To determine the capacity in cubic feet per minute (CFM) for a return register, you can use the relationship between the dimensions of the register and the velocity of the air moving through it.

First, you need to calculate the area of the register in square feet. Since the dimensions given are 20 inches by 30 inches, you convert these measurements to feet:

• Convert 20 inches to feet: 20 inches ÷ 12 inches/foot = 1.67 feet (approximately).

• Convert 30 inches to feet: 30 inches ÷ 12 inches/foot = 2.5 feet.

Now, calculate the area:

Area = Length x Width = 1.67 feet x 2.5 feet = 4.175 square feet (approximately).

Next, you multiply the area by the velocity (in feet per minute) to find the airflow in CFM:

CFM = Area x Velocity = 4.175 sq ft x 500 FPM = 2087.5 CFM.

This value reflects the capacity of the register, and when rounded to the nearest appropriate choice, it corresponds closely to the answer given. The reason the answer is selected is that it accurately reflects the computed airflow