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Today, I replaced the exhaust fan in my laundry room. I didn't realize that there is an insulated HVAC duct right next to the exhaust fan in the ceiling. As I was wrestling the old fan out, I tore a 3 inch long slit in the duct. It did tear all the way through, and I can poke my finger into the inside of the duct.

Note the the duct I tore is for the heating and air conditioning system. My exhaust fan duct was not harmed. Also, the location of the duct is in the ceiling between the first floor and the second floor (it is not in an attic).

As a temporary fix, I put some Nashua foil tape over the slit in the duct. I turned the furnace on and used my hand to verify that no air is escaping from the slit. Though, with the furnace on, the foil tape was slightly warmer than the rest of the duct. (No surprise - the foil tape is a much worse insulator than an insulated duct.)

Anyway, my question is: if I don't want my duct to leak, is it important that I do a more elaborate fix? Is the foil tape likely to come off on its own?

The more elaborate fix I am thinking about doing is to buy some insulated ducting material, put it over the foil tape that I already put on the duct, and then wrap more tape all the way around the circumference of the duct.

P.S. This is approximately the type of insulated ducting in my ceiling: enter image description here

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  • Did you put the tape on the outside of the insulation, or did you pull back the insulation and put the tape across the metal duct itself (or both)?
    – Nate S.
    Commented Jan 11, 2021 at 18:29

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Get a flex duct connector like is used to join two sections of flex together.

Cut completely through at the tear.

Fit the union into the inner sleeve.

Tape inner sleeve to connector.

Pull insulation back over the joint and tape well with duct tape.

If you want to insure it not pulling apart screw through duct tape with sheet metal screws around both sides into the connector. Another method very similar uses big zip ties to secure the insulation and vapor barrier. And screws and tape to secure inner sleeve to connector

This video shows it very well.

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  • I would not use sheet metal screws on flex usually tape and large zip ties is all I use tape and zip the inner duct pull the insulation and outer insulation over the fitting then zip tie the outer if the second zip tie is closer to the end I have not had one blow off even when the vents were closed and split a trunk line.+
    – Ed Beal
    Commented Jan 11, 2021 at 14:52
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    I agree that this is a great way to do the repair, but it begs the question - "is it necessary?" It is really necessary to go through all this , or is simply taping the outer plastic wrap sufficient? No, it's not perfect, but since the leak is in conditioned space, is it critical?
    – FreeMan
    Commented Jan 11, 2021 at 15:53
  • @FreeMan I took “in the ceiling” to mean attic. If it is between floors still would want complete seal and insulation to prevent condensation and mold growth from ac running.
    – Kris
    Commented Jan 11, 2021 at 15:57
  • Fair enough. My laundry room doesn't have attic space above it, so I didn't think of that perspective.
    – FreeMan
    Commented Jan 11, 2021 at 15:59
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    @Kris, Yeah, that makes sense. I will plan to get some metal ducting and do the technique from the video that you linked. And I will probably use zip ties instead of screws.
    – solvingPuzzles
    Commented Jan 11, 2021 at 22:05

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