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Thread: Duct Liner

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    Default Duct Liner

    we have already designed, sized, and modeled our ducts; we are now told we need to use duct liners not insulation. Is there any way to have Revit automatically increase the duct size to show the actual size of the duct while maintaining the inside clearance of the duct that is now defined by the liner? Otherwise we have to leave the duct the same size but then we get clash detection issues because we are not modeling the realistic size of the duct. Thanks for the help.

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    Default Re: Duct Liner

    Two quick thoughts...

    You could try applying duct wrap insulation, and playing with the display settings for insulation and duct, but I suspect you will have issues with hidden lines not behaving like you want.

    You could create a duct schedule sorted by width and height, and increase the sizes from the bottom of the list to the top. I suspect you will have issues with transitions at elbows and such, not to mention any tight bends not having room to be created once the size is increased.

    We are not allowed to use interior lined duct due to mold concerns. We are only allowed to use it on transfer ducts where we want to prevent noise transfer or for privacy.
    David Raynor
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    I could stop if I wanted to jlondenberg's Avatar
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    Default Re: Duct Liner

    Quote Originally Posted by rdooley944157 View Post
    we have already designed, sized, and modeled our ducts; we are now told we need to use duct liners not insulation. Is there any way to have Revit automatically increase the duct size to show the actual size of the duct while maintaining the inside clearance of the duct that is now defined by the liner? Otherwise we have to leave the duct the same size but then we get clash detection issues because we are not modeling the realistic size of the duct. Thanks for the help.
    The only good way of doing this is by just doing it right. Go through your ductwork, small areas at a time, and add lining and re-size. As David said, there will be adjustments in fittings to make along the way.
    Joel Londenberg
    Consultant - BIM Box Biz

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    Default Re: Duct Liner

    The problem with this is when you tag your duct it gives you a new larger duct size; industry standard it to give the inside clearance dimension, so if there is liner the contractor knows to order a larger duct size to accommodate the required liner to maintain the required inside clearance. If we resize and tag we are giving the wrong required inside clearance dimension, so the contractor will upsize from that larger dimension to accommodate the lining, which would result in the wrong duct; aka poor service and more money.

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    Default Re: Duct Liner

    A general note that explains what duct dimensions mean is also standard for a set of documents. The dimensions are correct for ducts that are not lined. Provide a extra marker (declaration) for lined duct conditions. Until Revit provides a way to redefine what duct dimensions to tag (when lining is used) we have to document our way around it. Contractors aren't as dumb as "we" seem to think they are, provide clear information and they'll be fine.

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    I could stop if I wanted to jlondenberg's Avatar
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    Default Re: Duct Liner

    You can also change your duct tag to reference the parameter "Free Size". This will be the correct inside dimension whether it is lined or not, no matter the thickness of the lining.
    Joel Londenberg
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    "The best you can hope for in this life is that your delusions are benign and your compulsions have utility." - Dilbert author Scott Adams

    This is the correct date format!

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    Default Re: Duct Liner

    Quote Originally Posted by ddraynor View Post
    Two quick thoughts...

    You could try applying duct wrap insulation, and playing with the display settings for insulation and duct, but I suspect you will have issues with hidden lines not behaving like you want.

    .....
    This is how we did it before Autodesk changed the way they did insulation and lining, primarily so that we could still show the free area size - contractors may be allright with a note, and generally use sheet metal size anyway, but government agencies are usually stuck in the dark ages and would accept changes to documentation standards about about 10 years after hell freezes over.

    The main problem with this is that you are still not accurately modelling what is going to be installed. Bending radiuses and actual fitting sizes will be wrong and you can't easily get sheet metal required and thus total price of ductwork.

    Since 2012 Revit has allowed the "Free Size" parameter to be used (as mentioned by Joel above) and thus designers can at least tag in the traditional way. I have long argued that ductwork should be able to be designed as free area as this is essentially what we have to do, however even if that was the case then you would still have to change small areas at a time as you would still get fitting sizes changing and possibly no longer connecting correctly.

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