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Old 11-24-2007, 03:04 PM   #1
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flex duck vs metal duck


I have always believed metal duck was better because:

1. air flow is better
2. uses less space

now some installers (who probably dont want to do the metal duck, even if I pay extra for it) are telling me that the flex duck is just as good or even better if done correctly.

Is that true?

Thanks to all you experts for helping us newbees out.

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Old 11-24-2007, 09:29 PM   #2
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flex duck vs metal duck


When sized correctly fex duct will indeed give the same airflow as sheet metal duct, the thermal conductivity of flex is lower than metal translating into lower heat gains or losses, its cheaper and easy to install compared to metal, at the same time flex is only suitable for attic installation, no allowed under some states codes and takes more room than sheet metal. I would pick metal work over flex without thinking twice, but thatís just my personal preference.

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Old 11-25-2007, 06:30 AM   #3
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flex duck vs metal duck


As a builder, I specify metal ducting only when crossing areas like a vaulted ceiling, where access later would be difficult. Otherwise, it is going to be flex duct, which is quieter, IMO.
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Old 12-20-2007, 04:21 PM   #4
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flex duck vs metal duck


If your installers are comparing metal & flex "ducK" then you need to find new installers ASAP.
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Old 12-20-2007, 04:40 PM   #5
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Old 12-22-2007, 09:10 PM   #6
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flex duck vs metal duck


Flex duct has more "R" value than uninsulated metal duct and can be run easier. Metal ducting offers less flow restriction (higher velocity) and doesn't wear out. You can have a 50' run of metal duct, flex maxs out at 14'.
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Old 12-22-2007, 11:30 PM   #7
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flex duck vs metal duck


I think flex duct is only used for supply though, not for returns, in all areas except the attic.
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Old 12-23-2007, 06:39 PM   #8
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flex duck vs metal duck


Quote:
Originally Posted by handy man88 View Post
I think flex duct is only used for supply though, not for returns, in all areas except the attic.
In the real world hacks try and use it as much as they can get away with.
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Old 12-23-2007, 07:30 PM   #9
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flex duck vs metal duck


Any one can install a piece of flexduct, only a true tradesman can bend and install sheetmetal.
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Old 12-23-2007, 11:26 PM   #10
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Quote:
Originally Posted by Chris Johnson View Post
Any one can install a piece of flexduct, only a true tradesman can bend and install sheetmetal.

Exactly, and that's how I feel about plumbing with flex tubing. It's a manufacturer's way to sell more product to people that can't install the real way.
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Old 11-05-2008, 11:57 PM   #11
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flex duck vs metal duck


My understanding is that here are two types of flexible duct to be contrasted with the rigid galvanized steel.

those two types are what I have heard called " alumiflex" and " wireflex".

the former is a system with a rigid aluminum tube core with insulation, and the latter is a continuous slinky like wire with a internal mylar like lining, and externally insulated to R6 or R8. My question is, in a n uninsulated crawl space below a house setting in a mild climate, which is preferable to use as conduits for hot air from a furnace? I have heard that the alumiflex is noiser but rodent safe, whereas the wire flex is quieter but easily chewed through by rodents. Which is more efficient?
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Old 11-06-2008, 12:14 AM   #12
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flex duck vs metal duck


Flex duct, like sheet metal duct, has to be sized coreectly.

If its not, it don't matter what its made from.
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Old 11-06-2008, 08:58 PM   #13
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I've seen too many instances where flex duct gets "abused" - sharp bends in the run reducing airflow, flex going up/down/around obstructions adding more resistance to the run, etc. One more vote here for sheet metal.
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Old 11-06-2008, 10:25 PM   #14
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flex duck vs metal duck


I prefer metal pipe. It has way more throughput secondary to more laminar flow compared to the same size flex duct.

Flex duct has too much non laminar flow with all its coils and bends. It also takes a lot more room. Insulating pipe is still smaller than flex.

Plus it's a lot easier to put in saddles and Y's.

Also I have never ripped metal pipe.
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Old 11-07-2008, 04:11 PM   #15
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flex duck vs metal duck


I think flex duct is great in the right applications. To say that a true craftsman only uses tin is kind of gutsy. I've seen some of the worst jobs you could imagine by guys who only use hard pipe. I also know that other trades appreciate flex for the fact that it allows them to get their stuff in a little easier than hard pipe. You may have never seen hard pipe tear but, have you ever seen it smashed by a plumbing pipe or an elbow broken off the main trunk because the hard pipe had no give? I think bottom line is the quality of contractor you use not the type off pipe you use. personally I use a sized and shop built supply and return air trunk, with flexible runs off of the trunk.

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