Code / constitutes plenum

Question 1. Does duct liner have to be sealed on all sides or just glued on the back ? 2. What constitutes a supply plenum ?

I’m being told 1. Code means work must be sealed on all sides

  1. Supply plenum connecting to ductwork versus supply plenum connecting to ductboard which contains ductwork.

See pictures please.


A supply plenum is an open space which is used as a means to supply conditioned air from the source through open or controlled vents.

This configuration is often seen in commercial or industrial settings, where the space above the suspended ceiling is pressurized, and the returns are ducted back to the handler.

It is not a typical configuration, as it often requires special ceiling considerations. Return plenums are far more common.

In both instances, the items above the ceiling, or in the plenum, needed to be rated as low smoke-producing items in the event of a fire.

I have seen it in lab construction and operation, where fumes from lab sciences cannot be returned through open plenums; they need to be ducted back.

Hope this helps.

Not sure what you mean by question 1, ‘duct liner’, if you are asking about acoustic insulation, a fiberglass duct liner covered with black fabric, all exposed fiberglass has to be sealed, including the ends. This is done by spraying glue on any exposed fiberglass. Prevents loose fibers from getting in the air stream.

Eric is correct.
Supply plenum can be a supply duct.
Is this the application you are speaking of?

THanks for your replies. If you see these pictures

Edges of the duct liner wasn’t sealed.

PArt of the plenum wasn’t replaced as you can see in the photos. If I was promised new supply adn return plenums would that include all of that?


I was just wondering if in the pictures its installed right? The edges werent sealed? also would the supply plenum / return plenum constitute the part in the pictures thats all kind of dirty and faalling apart? thank you

Looks like a mess, can’t tell if the edges are sealed, but it doesn’t look like it. Probably the supply plenum.