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Multi-Family closets used as plenums for split systems

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nuuvox000

Mechanical
Sep 17, 2019
344
I'm a little confused by the IMC as far as a split fan coil in the mechanical closets of apartments. The code clearly allows the closet to be used as a return air plenum but then all of the materials need to be plenum rated? I don't believe all of the components in the fan coil itself are plenum rated. Plus, there is typically a water heater in the closet as well which I'm sure has components that aren't plenum rated. When I ask manufacturers about this, they all give me a big "huh?" like they've never heard of something like this before but they all build equipment with "free-air" returns and sell thousands of these every year. Has anyone run into this issue before? Am I missing something simple in the IMC that allows the closet to be used as a plenum even though the unit itself is not plenum rated?
 
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No way I would sign off on such a design. You would be setting yourself up for a huge lawsuit if someone was injured or killed in a fire in such a plenum. Regardless of what the industry says, you had better protect yourself and license by strictly following the adopted code.
 
Other codes, like IBC, require plenum rating. You have to meet all applicable codes.
 
Simple solution is to nix the plenum.
Just a little duct connected to a grille would solve the problem.
Have to go thru the wall with the closet door? Use a half door and locate the grille below the door.
 
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