Ceiling Space Return Air Plenum

If this is an area used as a return it is normally referenced as a return plenum.

Ceiling space return air plenum.

This is most common in commercial buildings schools hospitals or libraries. In humid climates a cavity space used as a return air pathway will pull humid air into the cavity space possibly encouraging mold growth or the deterioration of building materials. Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum. Ceiling plenum 0 03 in.

Maintaining a low pressure drop return air path from conditioned spaces to the air handler can be a challenge using architectural plenums when spaces are divided by figure 1 figure 2typical pressures. Other common framing cavities used as return air pathways or plenums are air handler platforms open floor truss cavities and dropped ceilings. Fire protection within a return plenum is very important to the integrity of the entire structure and. However some drop ceiling designs create a.

The word plenum in the nec is used to describe both an air space and also various types of wiring methods that are specifically designed and tested for installation within these areas. Of thumb for sizing various return air transfer assem blies are shown in table 1. From reading 8 15 1 it seems vague on whether the plenum needs ductwork to the ceiling or leaving a portion s of the ceiling open to allow a return air unit to pull from the environmental space and thus pull from the occupied space. Dropped ceilings or suspended ceilings are often installed so that the space between them and the floor above or the roof deck can be used as a return air plenum.