In article , Randy Mahoney wrote:
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?

The cause is excess humidity. The solution, typically, is dehumidifiers in
basements, and vapor barriers and better ventilation in crawl spaces.
RAndy

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Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.