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Community and Q&A

Fabric flex duct?

bobbyarndt | Posted in Green Products and Materials on

I just got the rough-in completed on my HVAC system and was surprised to see a “fabric” flex duct used to connect the main trunk lines in the basement to the vertical supply stacks going upstairs but not on the return air coming back down.  I have only seen insulated or metal flex duct but this is a brown,  canvas-like material with metal or plastic ribs.  Feels like a synthetic canvas of some sort.

Has anyone seen this before or know what material this is?

Does anyone know why they chose this material over other types of flex?  Cheaper?  Something to do with fire stopping?

Just trying to figure out if it was installed with a specific purpose or if it’s a inferior material I should replace with something nicer.

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  1. Expert Member
    BILL WICHERS | | #1

    That stuff looks like what I see in commercial projects. It’s a fiberglass fabric, or at least usually is. This link shows an example (just the first place I found with a pic of what I’m used to seeing):

    There is an insulated version too. This is a good product, better than the cheapie plastic or foil stuff you commonly find in box stores. I doubt you’ll have any problems with it.

    Flex duct is less of an issue on forced air supply lines due to the positive pressure. Returns run under a negative pressure so it’s better to use rigid lines there. Admittedly, the difference is pretty small and I’ve both seen, and occasionally specced, short sections of flexible ducting on return lines before when necassary.

    Just make sure the flex duct is sealed well to the rigid ducting and don’t let them use plastic clamps for this (the plastic clamps tend to get brittle over time and loosen). It looks to me like your contractor used good quality materials for your project.


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