What is the term for the open space that carries air between the ceilings and floor above?

The correct term for the open space that carries air between the ceilings and the floor above is "Plenum." This area serves as a crucial component in heating, ventilation, and air conditioning (HVAC) systems, allowing for the distribution of air throughout a building. In a plenum space, air is circulated to and from various parts of the infrastructure, facilitating effective thermal management and air quality control.

Plenums are designed to accommodate the air supply and return needs of the building, often connecting ducts that distribute conditioned air or serve as a return air pathway for exhaust. Due to their role in ensuring air circulation without the obstructions commonly found in traditional ductwork, plenums can contribute significantly to the efficiency and performance of HVAC systems.

This understanding of a plenum is essential for professionals in fire safety, as it relates directly to the potential for smoke and heat movement during a fire. Proper design and maintenance of plenum spaces are critical for effective fire alarm and suppression systems, highlighting their significance in the context of building safety compliance.