Electric Water Heaters in Mechanical Closet Plenums 1

[nuuvox000]

The IMC doesn't technically allow water heaters in a plenum (in this case, a mechanical closet). It does have a line in there saying if something is non-combustible then it can go into a plenum. However, the definition for non-combustible is complex and requires some ASTM testing. The water heater is all metallic from what I can tell but none of the cut sheets from manufacturers say that it is plenum rated.

Have any of you run into this issue before? I'm in a situation where there is not space or a wall to run return ductwork in some small closets. The architect is saying that they have done this on other projects (I have seen this on other projects that were not my design as well). I might get with the plans examiner for the city and ask if they're okay with it but I really hate getting variances. Anything I'm missing here that allows water heaters in mechanical closet plenums?

Thanks for your help!

 

[EnergyProfessional]

Plenums are concerned with burn characteristic and smoke development. I assume the heater has an electrical box, insulation, some sort of plastic cover, foam insulation, plastic relay..... all things that could be of concern. You can ask JHA, but they often go by plenum-rated, or not.

 

[lilliput1]

You have to work with the architect to provide you with space to run return air ductwork within the closet to meet code requirement.