Ceiling Space Return Air Plenum

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.

Ceiling space return air plenum.

If this is an area used as a return it is normally referenced as a return plenum. Fire protection within a return plenum is very important to the integrity of the entire structure and. 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. 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.

Section 300 22 a of the nec provides information on the installation and uses of electrical wiring and equipment in ducts that are used to transport dust. Of thumb for sizing various return air transfer assem blies are shown in table 1. This is most common in commercial buildings schools hospitals or libraries. Ceiling plenum 0 03 in.

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. Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum. However some drop ceiling designs create a. Other common framing cavities used as return air pathways or plenums are air handler platforms open floor truss cavities and dropped ceilings.