A/C ducts sweating

Five years ago I had an A/C system installed in a 100 yr old 2 story house. For the downstairs unit, the contractor put in custom fabricated rigid sheet metal ducts. The interior of the ducts are made of a black rigid insulation type material. The exterior is sheet metal with mastic covering all joints and seams The system works well. Except... Last week, while doing some other work under the house, I noticed that condensate was forming and dripping from the ducts at numerous places. The A/C contractor has performed various tests on the system and it is operating as it should be, at least in terms of air temps. in and out, fan speeds, coolant levels, ect. My initial concern was/is that the moisture might be coming from inside the ducts. Potential serious mold problems. I don't thing this is the case though. The exterior or the metal ducts are very cool. We are in S. Texas where the humidity is high. So I'm guessing that the condensate is forming on the exterior. That is only serious in that eventually the ducts are going to rust through and have to be replaced. This is the first time in five years that I have noticed this problem. While I don't spend lots of time under my house, I am under there often enough where I think I would have noticed it before. So what is the cause? And what is the solution? Thanks
RAndy
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The cause is excess humidity. The solution, typically, is dehumidifiers in basements, and vapor barriers and better ventilation in crawl spaces.

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Doug Miller (alphageek at milmac dot com)
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Two options: (the condensate IS forming on the outside)
1. don't worry about it. 2. Insulate them on the outside also.
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Steve Barker







"Randy Mahoney" < snipped-for-privacy@suddenlink.net> wrote in message
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Think finished basement with ducts above suspended ceiling tiles which will be damaged by dripping water.
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Regards,
Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

under there. The house is on a hill. It is typically pretty dry, however we have had much rain this year and the rounnd under the house is damp. Can't do much about that. I am concerned about the duct work rusting prematurly where condensate is forming.
Randy
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Additional insulation on the outside with a new vapor barrier over the insulation should take care of it.
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Joseph Meehan

Dia \'s Muire duit
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