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Noticed a water leak stain in my ceiling in the drywall. Cut a hole and noticed water drops dripping from the joint of a metal round air duct. This duct leads to an external air vent on the side of my house. It is currently extremely humid on the East Coast And I suspect that is somehow related. My plan is to seal the joint with mastic and fiberglass joint tapeIs. Is there anything else that I should do?

PS: In the above photo I have removed one sheet metal screw so there is a visible hole there

  • Is the air vent an intake vent or an exhaust vent? – ThreePhaseEel Sep 3 '18 at 20:27
  • Is this an air intake duct feeding fresh air to the vicinity of a furnace or hot water heater, or an exhaust duct? Does the external vent have protection to keep rain out? If it's an exhaust duct, does it have some type of flap to seal it when air isn't blowing through the duct? You need to determine the source of the water (rain? condensation on the metal?). Are you sure it is coming from inside the duct rather than dripping down the outside and dropping off at that edge? (cont'd) – fixer1234 Sep 3 '18 at 20:37
  • The key is to stop the source of the water. Sealing the joint will just have it run to another joint, or even into equipment. If all efforts to find and stop the source fail, I would capture the water and get rid of it rather than sealing the joint. Let it drain into something that captures it and pipes it away with tubing to a spot where it can safely discharge (like through the wall to the outside). – fixer1234 Sep 3 '18 at 20:37
  • It is an exhaust duct from my dryer or HVAC. I have flaps on the exhaust. I think it’s condensation from inside somehow. Would sealing it with waterproof tape be bad? How would I install new tubing to drain it? – Chris Sep 3 '18 at 21:10
  • If my exterior flaps don’t move easily could that be contributing to the problem – Chris Sep 3 '18 at 21:16

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