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Need Help with Insulating HVAC ducts

novine | Posted in Green Building Techniques on

To qualify for some energy efficiency rebates, we needed to insulate 25′ of the HVAC supply ducts in our basement. I found this online that recommended using rigid Polyisocyanurate foam board to insulate the ducts.

We used duct mastic to seal the gaps in the existing duct work. Then we cut sheets of Super Tuff-R to the ducts to create a box (we used the board all the way around the duct as opposed to fiberglass batts on top). We installed the Super Tuff-R with the blue side out and the silver side facing the ducts attaching the pieces to the duct and each other with a UL 181 foil-backed. So far, so good. But a day after we finished the work, the tape is peeling away from the blue facing of the Super Tuff-R sheets. The tape sticks great when it’s applied to the duct surface but it doesn’t want to stay stuck to the blue Tuff-R surface. I did try burnishing the tape to get it to stay stuck but that hasn’t really helped.

Does anyone have any suggestions for a tape that will stick to the blue face of the Super Tuff-R pieces? Or any suggestions on how to attach the insulation so that it stays in place?

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  1. GBA Editor
    Martin Holladay | | #1

    According to advice on the Dow website (Dow is the manufacturer of Tuff-R), you want to use a foil tape manufactured by Venture. That's the same advice I gave in my article on the topic of tapes and gaskets.

    Here are links to two products that will work for you: VentureTape 1521CW (1.4 mil thick tape) or VentureTape 1520CW (a 2 mil thick tape).

  2. novine | | #2


    Thank you. I'll see if I can track down the VentureTape. I didn't see it available from our local home improvement stores but I'm checking with the manufacturer.

    I had also contacted Dow about the tape issue and they stated "The application in which you have used our product is not a supported application. This product needs to be covered with a 15-minute thermal barrier to meet code.". Any suggestions on how to address this concern? I know that others have used this material to insulate ducts. This document states that Super Tuff-R can't be used in basements. If that's the case, I sure wish I had known that a few days ago.

  3. metricus | | #3

    My experience with Super Tuff-R is that no aluminium tape would stick to it long term. I believe that the reason is the difference in the expansion coefficients of the AL and the "blue" substrate. Venture tape as well as the Shuretape found at Lowes will stick until cold hits it. then you will see it peeling off the tuff-R. It is also an overkill to use AL tape since the blue face of the Tuff-R is not reflective.
    I had great success with the Tyvek tape (Home Depot) used for house-wrap. It bonds great and the bond is not affected by temperature.
    If you use regular Tuff-R (with alumnium on both sides) then the Venture tape will work fine and makes more sense to use it since it is assumed that you need reflection on both sides.

  4. Aardal | | #4

    Longer lengths of standard grade foil tape tend to release when applied to the plastic film side of sheathing. Apparently due to expansion factors. Mastic type tape though more costly, is permanently pliable and will accommodate expansion to a greater extent.

  5. user-6184358 | | #5

    Use Thermax brand insulation-
    "This product needs to be covered with a 15-minute thermal barrier to meet code.". Any suggestions on how to address this concern?"
    go over all your work again with it has the 15 min thermal barrier laminated to the foam

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