In what location is the pinwheel rotor positioned for measurement?

• A. On the exterior of the building
• B. Inside the control panel
• C. In a separate room
• D. Mounted in the duct such that the rotor is in the center of the airstream

Answer: (D)

The pinwheel rotor is placed in the duct so it can sample the actual moving air. To get an accurate reading, it must sit in the center of the airstream where the air velocity is representative and not distorted by duct walls, bends, or obstructions. Mounting it in the duct with the rotor in the center of the flow ensures the measurement reflects true duct airflow. Placing it outside the duct, inside a control panel, or in a separate room would not encounter the moving air the duct carries and would give an incorrect or meaningless reading.