# sweating duct



## tommy henry (Jul 18, 2011)

what would cause duct work to sweat under a crawl space


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## refermadness (Jun 23, 2011)

not insulated correctly or blow by condensation, or condensation leak.


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## Vaporx (Jun 29, 2011)

refermadness said:


> 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.:001_unsure: Bad situation to deal with. Does the crawl have plastic vapor barrier laid down? That can make a big difference.


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## sktn77a (Aug 14, 2011)

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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## Spyke45 (Sep 26, 2012)

yep... damp crawl plus uninsulated ducts will cause sweating


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## WilliamR (Nov 14, 2012)

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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