What is a plenum?

In building construction, a plenum (pronounced PLEH-nuhm, from Latin meaning full) is a separate space provided for air circulation for heating, ventilation and air conditioning (sometimes referred to as HVAC). It is typically provided in the space between the structural ceiling and a drop-down ceiling. A plenum might also be under a raised floor. In buildings with computer installations, the plenum space is often used to house connecting communication cables.

In the U.S., typical plenum cable sizes are American Wire Gauge (AWG) sizes 22 and 24. Plenum cabling is often made of Teflon and is more expensive than ordinary cabling. In the event of fire, its outer material is more resistant to flames and, when burning, produces less smoke than ordinary cabling. Both twisted pair and coaxial cable are made in plenum cable versions.

This was last updated in May 2024

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