The speed at which air exits a fan is measured in which unit?

• A. Miles per hour
• B. Meters per second
• C. Feet per minute
• D. Kilometers per hour

Answer: (C)

Air velocity is distance moved per unit time, and for air exiting a fan the common practice is to express this speed in feet per minute. This unit fits well with how duct sizes, friction losses, and fan performance data are specified in RETA and U.S. HVAC work, giving a convenient, intuitive scale for typical duct velocities and for reading charts or specifications. While meters per second is a valid scientific unit and used in metric contexts, feet per minute remains the standard in this field. Miles per hour or kilometers per hour are geared toward road speeds and aren’t practical for the fast, narrow flows in ducted air systems. If you’re ever more comfortable with metric units, you can convert—1 meter per second is about 196.9 feet per minute.