sweating duct

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Old 07-18-2011, 01:55 PM   #1
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sweating duct

what would cause duct work to sweat under a crawl space

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Old 07-18-2011, 03:52 PM   #2
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Re: sweating duct

not insulated correctly or blow by condensation, or condensation leak.
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Old 07-19-2011, 08:48 AM   #3
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Re: sweating duct

Originally Posted by refermadness View Post
not insulated correctly or blow by condensation, or condensation leak.
..or high humidity in the crawl. My house is on high ground, the crawl is dry and the duct (1" board and wrap) doesn't sweat. But the same ductwork can sweat in other crawls. Bad situation to deal with. Does the crawl have plastic vapor barrier laid down? That can make a big difference.
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Old 08-14-2011, 05:11 PM   #4
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Re: sweating duct

The duct surface temperature is lower than the dewpoint under your house. Humidity is too high for the duct temperature. Reduce the humidity (plastic on teh ground, dehumidifier) or increase the duct surface temperature (increase air flow). Most codes call for sealed crawlspaces in new construction now to avoid this (condensation can cause mold).
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Old 09-26-2012, 08:00 PM   #5
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Re: sweating duct

yep... damp crawl plus uninsulated ducts will cause sweating
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Old 11-15-2012, 10:24 AM   #6
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Re: sweating duct

Yeah, you'll need to raise the surface temperature of the ducts or maybe consider some way to regularly dehumidify the problematic area.
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