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My contractor left two screw holes in one of my insulated supply duct lines (because they had added a strap to hang new ductwork on, but they changed their mind and moved it). What's the best/easiest way to plug it up? It's in a hard-to-reach spot between and behind the new ductwork and when I tried putting a small sheet metal screw into it the hole using my finger tips, the hole was bigger than the small screw. So in the meantime, I put aluminum tape over the holes on top of the insulation but I'm afraid the supply air would continue to just leak into that insulation layer instead with just the tape.

Should I find a thicker screw and use that to plug it up? Or, should I just get some duct sealant or ducty putty and shove it into the hole through the insulation, then tape over that? Since it's hard to reach, I can't get my full hands through the tangle of ducts to do an adequate cut of the insulation to get to the bare metal beneath. However, I can just barely get my finger tips through so may be able to hand insert a screw or get some tape on or putty on it with a stick.

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    Photos would help a lot here -- to show the size of the duct and insulation and hole and surroundings.
    – Armand
    Dec 14, 2022 at 19:46
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    Call the contractor back and ask him to fix his mistake?
    – FreeMan
    Dec 15, 2022 at 14:13

4 Answers 4

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Poke the tip of a tube of silicone caulk in there and dab the hole, then patch the insulation with foil tape as you had done.

Really, those holes are inconsequential. There are probably a hundred such leaks in your system already. (Ducts weren't sealed like that until very recently--they were just sheet metal folded together.)

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I think you have already done enough with the Aluminum tape. That should keep the air from leaking out and that's what such tape is designed for.

If the duct is covered with insulation, then you should cut a small opening, cover the hole in the duct, and then replace the insulation and affix it with some tape.

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    wouldn't it just leak into the insulation layer since there is still a whole in the duct and a gap between the tape and the hole?
    – MonkeyBonkey
    Dec 14, 2022 at 19:24
  • Had to read a few times; so you did not tape the actual metal holes, but I stead the insulation surrounding the duct work with the holes?
    – Chris
    Dec 14, 2022 at 19:32
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    @Chris Yes, that's how I understand it - the holes in the metal duct are still open.
    – Armand
    Dec 14, 2022 at 19:45
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    It would still not really be a problem. If the heat is entering insulation then getting blocked from exit by tape, then it would form and air bubble stopping further air entering. And because it is an insulated air bubble, it would not affect anything, so sticking with jwh20 answer
    – Chris
    Dec 14, 2022 at 19:50
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Easiest way to plug screw holes when you don't care about the back side is to reinstall the screws, or go up a size if necessary.

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You could put a rivet in each hole to permanently block it, or add the strap as originally planned. More than the minimum retention strapping is not a bad thing.

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