Junction Boxes in cold air return

Old 08-18-14, 06:08 AM
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Junction Boxes in cold air return


I am replacing the lighting in my kitchen and I ran into an unexpected cold air return. The cold air return is just the joists with the drywall ceiling making up the bottom and the floor above making the top.

The problem is this is in the worst location possible. It runs directly over my island. My plan was to put a couple pendant lights over the island and a couple recessed lights up. I found the cold air return when I cut the hole for the recessed light that falls in this area.

What are my options? I really want to keep the lights in this area with the cold air return. Otherwise, I would probably have to scrap the whole thing and just keep my 1 inadequate light in the center of the room.

Can I create a box out of wood and/or drywall around the fixtures? I would probably have to tear up the ceiling a little more but that is ok. I saw someone suggest to just use a "metal metal junction box, metallic wiring method like MC or AC cable or conduit and caulk the openings". Is this ok? Is there one approach that is better than another? I want to make sure I am not breaking any code.

Thanks for any advise.
Old 08-18-14, 07:27 AM
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Welcome to the forums!

You can not have a plastic box or NM cable in a return air space. Except if the cable is just passing through the space. You could build a box around one but that might be more trouble then it is worth.

Your other information is correct. A metallic wiring method is your best bet. This is what is done in most commercial return air plenums. Using a metal box and either sleeving NM cable with flexible metal conduit/EMT, or using another metal wiring method such as EMT, FMC, MC/AC cable would be acceptable. If you do use a metallic wiring method, be sure to properly bond/ground everything. While caulking the holes of the box is not required, there would be less air leakage if you did.

I also see no reason you can not use recessed cans as they are also metal. Again air tight ones and metallic wiring method would be required.
Old 08-18-14, 09:51 AM
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can you install a piece of flex duct?

can you move the duct?
Old 08-18-14, 05:07 PM
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I don't believe there would be all that much air leakage to be concerned about,commercial building many times use air handling fixtures as part of the return air system, certainly use MC and metal boxes.

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