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Old 04-14-2010, 10:30 AM   #1
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Insulated flexible heat duct

Any thoughts on using this for the entire job down in my crawl space? I already have it on three runs off the old ductwork I'm removing. The flex part is only a few years old, so I plan to keep it where it is. It'd sure make my job easier, I would think. Anyone know of any on-line tutorials? EZ-install sites or similar?

Thanks guys! I googled it, but didn't find much.
(Searched here too, of course, same thing.)



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Old 04-14-2010, 03:02 PM   #2
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Flex can be used for both a trunk line, and for supply branches.
Some areas interpret the code on flexible duct connectors to include flex duct. It doesn't. but those areas won't let you use it for a trunk line.

Flex duct needs to be installed using a flew duct FR chart. Not the standard FR chart for sheet metal.


6" sheet metal pipe at .08" FR will flow 100CFM.
6" Flex duct at .08" FR will flow 75CFM.


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Old 04-14-2010, 03:04 PM   #3
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I know you need the next size up and the flex should be no sharp bends and stretched out to be efficient:

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