I'm having a pretty serious problem. There is an old sheet metal HVAC duct in my home that is getting condensation that is dripping onto the ceiling of a pantry. This duct is completely internal to the house, there is no exterior wall. The home was built in the mid 80's, modern style construction with lots of little half floors, so there is quite a bit of open space. There is a picture attached to this message.

I cut a hole into the ceiling and got rid of the damp drywall so I could access the duct. My hope was to wrap duct insulation around it, but it butts directly against an interal wall and header, making a wrap around nearly impossible.

Any suggestions on how I can get rid of this issue without breaking the bank or gutting the inside of the house?

In the image, the duct in the foreground runs horizontally, the other part is actually vertical up to the air handler, which is in a closet.

enter image description here

  • Is the air handler downdraft or updraft? Is the condensation coming from the inside and leaking through the seam or is it forming on the outside? Is it only in this one section? Commented Jul 2, 2018 at 21:46
  • This air handler is downflow, so these are the supply ducts. The horizontal one runs over the header for the closet door and runs down a framed area. Just outside the closet door is another spot that is leaking, and I can't determine if this is from the same source or from a separate area. The leak in this section at least seems to start at the corner of that horizontal seam on the vertical duct, visible in the picture.
    – J Astin
    Commented Jul 2, 2018 at 21:53
  • 2
    Is the condensation collecting in unconditioned space and dripping down the duct, or forming in conditioned space? Does the duct go through an unused area of the house where you have all of the vents closed? There should not be enough humidity in the conditioned space to get condensation. I suspect that it is either forming in unconditioned space and dripping, or water is coming from somewhere else (a leak in the structure), and finding its way to the duct. If it is condensation, you should see it evenly all over the surface of the duct.
    – fixer1234
    Commented Jul 2, 2018 at 21:54
  • The entire area in the picture is conditioned space, near as I can tell. It is entirely internal to the house at least. The condensation does not appear uniform over the entire duct, but the drip only occurs when the AC is running; rain does not leak here. The ceiling in the picture is the floor of the 2nd floor.
    – J Astin
    Commented Jul 2, 2018 at 21:57
  • 1
    I would suspect that condensate from the evaporator coil is not being carried away. It is getting into the ductwork. Check your condensate lines. There should be a service panel to the A-coil, but first see if you can insure that the primary condensate line is unobstructed. Can you see water dripping from the condensate drain? Commented Jul 2, 2018 at 22:09

2 Answers 2


I just had this same issue it was resolved by setting my fan higher setting and changing the dirty filter


Insulate the duct. This is the main way to prevent condensation on the duct work. If the duct is colder than the air in that space it will draw the moisture out of the air just like a glass of ice water. Insulation is the only way to stop this from happening running the fan faster won't stop condensation and may reduce the system efficiency.

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