In this article, we will explore what a plenum box is, how it functions within an HVAC system, key considerations in its design, and why proper selection is essential for optimal ventilation outcomes. What is a plenum box and how does it work? The plenum box is essentially an air. In HVAC systems, plenum boxes are essential components designed to convert dynamic pressure into static pressure, ensuring uniform airflow distribution while reducing noise and pressure loss. Search by air flow, pressure drop, terminal air velocity, supply temperature, max sound power level, and more. One crucial yet often overlooked component in this process is the plenum box.