I recently inspected a house that I am rating and discovered the HVAC contractor used Big 8 bubble wrap on the metal main duct in a vented attic in Climate zone 5. I spoke to the contractor about this at the rough inspection and duct testing and told him he needed to add more insulation to the nice wrap job he had done. My experience has been that a materiel that thin + a thin air space can not be classified as a R-8. I found a few articles from some pretty knowledgeable building science guys to confirm my thoughts. The contractor however is insistent that this is a suitable method of insulating duct work. He sent me the manufacturers claims and I looked up a ESR -report. (ESR-1236).  First I must say I do not work on really any new buildings with duct work outside the thermal boundary and advised agaisnt it! 

What is the industry accepted method for crediting duct work wrapped with a radiant barrier and a airspace.?The ducts did pass a total leakage test, but they still leaked so, it is not in a vacuum either. I could not find any official language by RESNET or IECC on this.

Thanks for your Thoughts in advance!

Duct Insulation specification.pdf

ESR-1236 Big 8 duct insulation.pdf

The Foil-Faced Bubble Wrap Sham - Understanding Radiant Barriers.pdf

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  • On a tangentially related topic:

    I saw this today in an old attic installed AC system. Ducts made from only fiber-board, coming apart at the corners.

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    • If you look closely ... can you see rat or mice teeth marks on foil?   Some of the modern materials are gourmet meals for rodents.   E.g.  they really enjoy a snack on some PEX  or the insulation from some automobile wiring...

      • Hmm, good point. I didn't notice any droppings but it could be. I'll check my other pics.

        • Pests are also a really good reason to seal duct work with either the approved mastic OR aluminum duct tape... not the sticky "un-Duct" tape that DIYers use... "un-Duct" can be tasty for some critters...

          To the right of your hand.... it looks like droppings...(?),  when I enlarge photo, it looks like chew marks.   

          Also another reason to where mask when going up into an attic......

  • I’ll give you an a for effort but even in the best cases bubble wrap ( unless it comes with a certificate of testing and depending on what lab was used) means nothing.
    If you can get a engineer’s stamp with signature maybe that might carry some weight, good luck
    GP Master Hvac contractor
    • I believe one of the issues is how does one defend themselves against an HVAC contractor that insists it is okay.   And the answer to that would have to be pull articles from ACCA or AHRI which say that reflective bubble wrap is worthless for duct insulation.  Otherwise it simply becomes a dispute between the trades.

      As an engineering type - I can argue that for duct insulation it is nearly worthless most of the time because the installers often don't understand the limitations and HOW IMPORTANT the strict adherence to the installation instructions are.  For example without the spacers and the 1" air gap all around the duct... the manufacturer's own claim for R-value drops from R-8 to R-6.

      I really doubt that the installer is able to certify that the installation instructions were absolutely followed without any deviation. 

      Also from about nine years ago - this discussion on greenbuildingadvisor

      https://www.greenbuildingadvisor.com/question/is-bubble-wrap-duct-i...

      At the time - not Energy Star approved and not approved for ACCA manual D.

      Is bubble wrap duct insulation Energy Star approved, and is it a good idea?
      I spoke with a HVAC installer who said he wanted to insulate my ducts with double-wrapped bubble wrap as a cheaper way to achieve R6. Does this stuf…
  • As a radiant barrier manufacturer I've been fighting this bad information for years. I've run into this claim for installing radiant barrier in attics many times.  Which is similar the claims made for wrapping ducts.  This is a video I did back in 2011 explaining how companies claim to get an R-11 with a 1/4" thick product. AtticFoil Compared To Bubble Foil Products

    • I think Ed and his video hit on an important point -- these radiant barriers are primarily addressing radiant energy.  They aren't doing much to address conduction losses and, if not installed properly, will not address convection losses.  And let's face it, its difficult and unlikely to get a "proper" installation in the field.

      If you are still seeing duct losses, this bubble wrap insulation is not installed "properly" (i.e. the air leakage from the duct is also leaking out of the Big 8 Duct Insulation) and therefore will not be able to achieve the claimed R-value.

  • Read the manufacturers claims and installation steps closely  The foil needs a dead space 

    "To achieve a thermal resistance of R-8, 2-inch-wide spacer strips of rFOIL™ reflective foil insulation are wrapped around the duct to create spacers at 2-foot intervals. The Big-8 duct insulation is wrapped around the duct with the spacers creating an airspace between the duct and the insulation. All seams and joints are sealed using rFOIL Metalized Tape (see Figure 5 of this report)."  from the duct installation instructions."

    If the installation is in a hot & humid climate -- that dead space could very well mean a place for moisture to condense when the air hits the duct... and that could mean water pooling and collecting between the duct and the foil.   Potentially perfect conditions for mold over time.  If the water leaks,  it can damage the building materials it resides on or around it.   Problems with condensation on the outside of cold ducts has been documented sufficiently enough to call it into question.   Those issues lead to additional research - as noted below (BTO)

    The DOE through the Building Technologies Organization (BTO) and the Build America program has done testing on buried ducts... and the technique that works well  -- is foamed ducts (to keep air away from the duct work) - then burying them in insulation --OR- just making sure that all ducts are in the climate controlled space to begin with...

    I'm with Sean Lintow -- while you can measure the R value in a lab for testing... there are simply too many ways it will fail when installed in the field... especially if the installers take short cuts or get sloppy.

    • @Dennis, without defending Big-8, I would point out that condensation (on duct surface) is a function of how well the vapor barrier (the outer layer) is sealed. This issue is exactly the same with conventional foil-faced fiberglass duct wrap. It, too, must be properly sealed at every seam and termination, otherwise condensation will form on the duct surface in all but the driest climates.

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