DIY Projects

How to Repair Leaks in HVAC Ductwork

By: Danny Lipford

Leaks in HVAC ducts allow air from your furnace or air conditioner to escape, wasting energy and raising heating and cooling costs.

To seal holes or tears in ductwork:

  1. Locate Leaks: Turn on the HVAC fan and feel along the ducts for drafts that indicate escaping air.
  2. Seal Leaks: Turn off the fan and apply special metallic foil tape made for repairing ducts over the hole or gap. Don’t use standard duct tape, since the adhesive will come loose over time.
  3. Apply Duct Mastic: Use a brush to apply duct mastic over the tape and joints to improve the seal.

Watch this video to find out more.

Further Information

Video Transcript

Leaks in ductwork are often found where lines branch off or separate. With the furnace fan running, you can feel air escaping the duct. Once you’ve found the leak, use foil duct tape to cover the gap and seal the leak.

For an extra layer of protection, use a paint brush to apply a coat of duct mastic. This thick, sticky material will dry to form an airtight seal that will keep the air in those ducts where it belongs.


Please Leave a Comment

9 Comments on “How to Repair Leaks in HVAC Ductwork”

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  • Official Comment:

    Thomas Boni Says:
    February 13th, 2019 at 7:49 pm

    Hi, Cw,
    Replacing just the crushed section and seaming it into the rest of the ductwork is your best bet.
    The cost will vary, based on location, but an HVAC tech could probably do it in an hour or so.
    Good luck with this project!

  • Cw Fields Says:
    February 13th, 2019 at 1:50 pm

    In May of last year I had a new a/c unit installed in an older home in central Phoenix. On a property inspection tenants complained the two bedroom in that house were colder than the rest of the house. On an inspection in the attic two lengths of ductwork leading to bedrooms, spanning approximately 12 feet, have been partially crushed due to workers stepping on them. The ductwork is approximately 24 inches wide with a height of 18 inches. Is there a way to fix the damaged portion using some kind of inflatable bladder inside the duct work or does it have to be completely replaced. Any idea of cost would also be greatly appreciated. Thanks,Cw

  • Official Comment:

    Thomas Boni Says:
    December 17th, 2018 at 3:21 pm

    Hi, Dixon!
    What a great question! We recommend submitting unique questions like yours to the Today’s Homeowner Radio Show.
    Please use this form to contact Danny Lipford, America’s Home Expert, directly:
    Take care!

    December 2nd, 2018 at 7:36 am

    I have noticed that if my heat or AC is on it runs smoothly with no problem. However after few minutes of running (approximately 15 minutes) the system automatically stops running and there is a heavy banging sound that is immediately heard above the ceilings where the ducts are . this large banging sound can be heard through out the house. This banging sound does not come on when the system automatically starts running again but will do only when it is about to stop. What can I do to stop this heavy banging sound in my house while the AC/ Heat system is operating?

  • Official Comment:

    Thomas Boni Says:
    November 16th, 2018 at 5:50 pm

    Hi, Pat! We used Nashua FlexFix for this project. It should be available at your local The Home Depot.
    Take care!

  • Pat Says:
    November 16th, 2018 at 4:23 am

    What is the brand of duct masking and when can I buy it? When I search it comes up with duct tape.

  • Official Comment:

    Thomas Boni Says:
    August 14th, 2018 at 1:07 pm

    Hi, Bev,

    You know what they say — a picture’s worth a thousand words! Please send photos to so we can better understand your question.


  • Bev Says:
    August 13th, 2018 at 8:54 pm

    Apartment was bug bombed in the trash room and inside of walls. I want to know if it can get into the AC or ducts causeit has a chemical odor I used bleach to clean coils can I get rid of it with water and brush?

  • daniel w hebert Says:
    March 14th, 2017 at 8:52 am

    what is an RAPP boot? I have this notes on a set of specs.
    what do you recommend for lighting rods which penetrate a metal roof?

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How to Repair Leaks in HVAC Ductwork