In a calculation to determine face velocity, what do you divide the CFM by to find the result?

To determine face velocity, you divide the cubic feet per minute (CFM) by the free area in square feet. This calculation gives you the speed of air moving through a cross-sectional area of the duct or outlet, expressed in feet per minute (FPM).

Face velocity is a critical parameter in HVAC system design because it helps determine how effectively air is being moved through the system. A higher face velocity typically indicates more air is being distributed in a given area, which can be beneficial for performance but may also lead to increased noise or wear on components.

Using the free area in square feet is essential because face velocity fundamentally relates airflow (volume per time) to the area through which the air flows. Dividing by the area allows for a straightforward measure of how fast the air is moving across that area, which is vital for ensuring the system operates efficiently and effectively.