Air conditioning ducts to 2nd floor run between ceiling joist of 1st floor.
Have developed water stains on ceiling.These stains are the result of
Condensation forming on the ducts and leaking through the ceiling dry
Wall. What needs to be done to stop this from happening. Open for
Suggestions.

That duct is in the cold part of the house, so it really shouldn't be getting any condensation on it. However, since it is.. .

If you want to be sure that you'll never get condensation on that duct, you need to insulate it. For A/C installations, there is an insulation with a silver waterproof barrier on one side. Wrap the duct with the insulation, silver side out. It works just like vapour barrier in your exterior walls. You need to keep the moist air outside of the dew point. You'll have to get some special tape to seal the seams on the insulation as well.

Quote:

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Originally Posted by dmatos

That duct is in the cold part of the house, so it really shouldn't be getting any condensation on it. However, since it is . . .

If you want to be sure that you'll never get condensation on that duct, you need to insulate it. For A/C installations, there is an insulation with a silver waterproof barrier on one side. Wrap the duct with the insulation, silver side out. It works just like vapour barrier in your exterior walls. You need to keep the moist air outside of the dew point. You'll have to get some special tape to seal the seams on the insulation as well.

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Hello friends. I have a question about this problem. Can we prevent this condensation without using insulation material in pvc ducts. What do you think ?

Sure if you have enough air changes at a high velocity. LOL. Cold surfaces and high moisture causes condensation. If you remove the moisture by other means then the condensation problem will go away. Also if you raise the operating temp of the duct the moisture problem will also go away. Plastic/PVC ducts will offer a insulation factor but the flame spread and smoke density will kill you in a fire. NO PVC ducts in my home. LOL