Ceiling Space Return Air Plenum

Of thumb for sizing various return air transfer assem blies are shown in table 1.

Ceiling space return air plenum. Fire protection within a return plenum is very important to the integrity of the entire structure and. 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 plenum 0 03 in. This is most common in commercial buildings schools hospitals or libraries.

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. 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. 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. Other common framing cavities used as return air pathways or plenums are air handler platforms open floor truss cavities and dropped ceilings.

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. However some drop ceiling designs create a. 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. 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.