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thesuaves22 07-21-2013 04:13 PM

Duct box between floors is condensating = wet ceiling
I have a two story house and all of the ducts are run from the attic. In the ceiling above the first floor there is a metal box, with several ducts run from it to all of the registers in the ceiling on the first floor.

Friday night, I noticed the ceiling was wet in a spot on the first floor. So I cut a hole in the ceiling to find that metal box that distributes the air to the first floor registers was sweating A LOT. After the moisture was wiped from the exterior of the box, the sweating stopped.

We've had some really hot and humid days here in central NC, and my AC system has been running a lot, but doing a great job of cooling the house.

I bought some duct insulation with the plan to wrap the outside of the box to prevent the condensation. Is that the best solution? What else should I do to prevent this from happening again?

FClef 07-21-2013 05:28 PM

Insulating the box should do it. If you have either a vinyl insulating wrap or fiberglass duct board that will work the best. Leave no metal exposed. Also make certain that the area is good and dry before insulating, you don't want to trap that moisture.

joecaption 07-21-2013 05:37 PM

Also make sure there's no leaks at the seams.
If there is, use foil duct tape to seal it up before the insulation not "duct tape".

thesuaves22 07-21-2013 10:52 PM

Thank you both for your replies! I do have a bunch of the expensive hvac silver tape leftover from a previous project.

I was planning to use this stuff:

I was planning to use the roll fiberglass insulation to cover the box instead of the board simply because it would be easier for me to work with in the ceiling to get around the nooks and crannies.

I'm unable to get to the top of the box since it is mounted flush on the flooring of the second story. I only have about a foot of room to work since there are web trusses between the two floors.

thesuaves22 07-23-2013 10:53 PM

Had a guy come over with a camera snake tool tonight and drilled a small hole in the box and saw the inside of the box was not insulated at all. So there's a sheet metal box that the builder put between floors of my home without insulating the inside or outside of the box. :furious:

At this point is it better to insulate the inside like most supply boxes are insulated? I'll likely have to replace it, I guess. There's no getting around the fact that it has to come down since I can't get to the top of the box to insulate it.

Any advice? Thanks everyone

PoleCat 07-24-2013 05:11 AM

Looks like a job for spray foam.

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