What is the first step to calculating the CFM capacity of a return register?

The first step in calculating the CFM (Cubic Feet per Minute) capacity of a return register is to calculate the total area of the register. This is crucial because the CFM capacity is dependent on both the velocity of the air passing through the register and the area of the register itself. The area allows you to understand how much air can flow through that opening, which is a key factor in determining overall airflow.

Calculating the area provides the necessary dimensions to apply the airflow equations that relate velocity to CFM. Once you have the area, you can then measure the velocity of the air flowing through the register and utilize the formula for airflow: CFM = velocity (in feet per minute) x area (in square feet). This logical sequence ensures that you gather all the necessary information to arrive at an accurate CFM calculation.

While it is important to measure velocity, convert square feet to square inches, and understand the type of register, these steps occur after you have determined the area of the register.