Ceiling Space Return Air Plenum

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.

Ceiling space return air plenum.

Fire protection within a return plenum is very important to the integrity of the entire structure and. A plenum space is a part of a building that can facilitate air circulation for heating and air conditioning systems by providing pathways for either heated conditioned or return airflows usually at greater than atmospheric pressure. This is most common in commercial buildings schools hospitals or libraries. Ceiling plenum 0 03 in.

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. 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. Normally the space above the ceiling and the deck above is used to return air from the conditioned spaces below the ceiling to the air handling equipment. Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum.

If this is an area used as a return it is normally referenced as a return plenum. However some drop ceiling designs create a. Of thumb for sizing various return air transfer assem blies are shown in table 1. Other common framing cavities used as return air pathways or plenums are air handler platforms open floor truss cavities and dropped ceilings.