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Old 11-09-2008, 09:17 AM   #16
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flex duck vs metal duck


As an HVAC designer metal duct is prefferable over flex. Metal duct creates less drag and maintains a better velocity when installed properly. Flex ductwork is recommended in attics or spaces that are not conditioned. The pre-insulated flex duct does hold the heat and cooling better than bare metal duct. You can purchase duct wrap which would allow you to achieve the same insulation factors as flex when wrapped around the metal duct. Flex duct is alot easier to install than metal making it more cost effective at the quote phase of the project. If you are putting in a new system and the duct is being intalled in a basement or conditioned space insist on metal trunk and metal supply branches for a more effective system. Flex is ok as long as it is installed properly with the correct strapping... once flex starts to sag that is when you lose efficiency. Also you want to avoid any flattening of the flex or kinking. There is a reason why most commercial projects only allow a maximum of 6' of flex to the supply grills and the rest must be galvanized metal from the main trunk.

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Old 12-18-2011, 11:35 AM   #17
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flex duck vs metal duck


After reading this thread, if I were to replace the spiral wire flex duct with rigid, do I go 1" lower in diameter? My home has the flex for the branches running to floor boots.
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Old 12-18-2011, 01:21 PM   #18
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flex duck vs metal duck


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Originally Posted by bob22 View Post
After reading this thread, if I were to replace the spiral wire flex duct with rigid, do I go 1" lower in diameter? My home has the flex for the branches running to floor boots.
No, stay same size.
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Old 12-18-2011, 01:28 PM   #19
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flex duck vs metal duck


Would flow improve to be worth the time/investment? The span is about 15' from trunk to boot.
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Old 12-18-2011, 03:16 PM   #20
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flex duck vs metal duck


Probably.
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Old 12-18-2011, 07:29 PM   #21
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flex duck vs metal duck


each has to be installed right to the way it was designed...and as beenthere said... if not sized right...dosen't matter what is used..
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Old 12-19-2011, 06:30 AM   #22
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flex duck vs metal duck


Thank you both!

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