Plenum Ceiling

I know we need the rain out here in California, but with baseball season fast approaching, get it out of your system Mother Nature. Opening Day for the major leagues is just 26 days away, the World Baseball Classic has started, and college baseball has been playing for a few weeks. I must say congratulations to the San Jose State Baseball Team which is now 9-0 to start the season and and is ranked #25 in the nation.

For those of you who took the poll in my last post, “my record” is the San Jose State Career Homerun Record.  Congratulations if you selected the correct answer.

Air Return Vent From Below

On a recent job I was able to get a picture of a plenum ceiling that I wanted to share. 

The picture to the right shows the air return vent, most offices will have something similar to this.  So if most offices have this, what determines if it is a plenum or nonplenum ceiling?

The answer is in the ceiling above this vent.

The picture below is of this same vent, but from the ceiling space above.  As you can see, there is nothing connected to this vent.  Which means air flows from inside the office, through this vent and into the ceiling space and eventually makes its way to the HVAC unit.

Air Return Vent From Above

If the ceiling space is used for air handling, it is a plenum space.

However, if there is a duct connected to the vent for return air, as in the picture on right, it is a nonplenum space.

Air Return with Duct - Nonplenum Space

Unfortunately, it’s not always easy to determine from the floor below, and often requires climbing a ladder and poking your head up in the ceiling space.  Keep these pictures in mind when you’re trying to determine if a ceiling space is a plenum space or not.

So, why should you care if a ceiling is a plenum space or not?

Well, when it comes to voice and data and audio/video cabling, non-plenum cable is significantly cheaper than plenum cable.  And until recently, plenum rated HDMI cables haven’t even been available.

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