Connection between grille and distribution box

A grille connects to a distribution box (plenum) via a spigot or flange, allowing controlled airflow from the duct system into the room while enabling measurement and adjustment of air volume.Mechanical ConnectionGrilles are typically attached to plenum boxes or distribution boxes using spigots, which can be circular, rectangular, square, or flat oval depending on the system design . The spigot often includes grooves or spring mechanisms that allow the grille to lock securely into place . This connection ensures that the grille is properly aligned with the airflow path and can be easily detached for maintenance or adjustment.Airflow Control and MeasurementMany plenum boxes are equipped with measurement and adjustment modules (e.g., MSM or MEM units) that allow technicians to measure differential pressure and calculate airflow rates . The grille must be connected to the plenum in a way that does not interfere with the control spindle or measurement tubes. Airflow can then be adjusted by rotating the control spindle, and the damper position can be locked to maintain the desired flow rate . This setup ensures accurate airflow delivery to the space.Noise and Pressure ConsiderationsThe plenum box reduces duct pressure and air velocity, distributing air evenly across the grille face and improving air distribution quality . Proper sizing of the plenum relative to the grille is important because grilles have low air resistance compared to the ductwork, and incorrect sizing can lead to noise or uneven airflow . Low-velocity stub ducts or direct plenum connections are recommended to maintain efficiency and minimize noise.Installation NotesEnsure the grille is detachable for access to the plenum's measurement and adjustment modules .Maintain recommended upstream distances from the plenum to ensure reliable airflow measurement .Use appropriate fasteners or spring clips to secure the grille without bending the control spindle .Consider thermal or acoustic lining inside the plenum to reduce noise if required . In summary, the grille serves as the visible outlet for conditioned air, while the distribution box or plenum acts as the intermediary that controls, measures, and evenly distributes airflow from the duct system. Proper connection ensures efficient HVAC performance, accurate airflow control, and reduced noise.