How To Seal Ductwork

Do you feel like you’re throwing your money out of the window with your heating and cooling system? You probably are – through cracks, leaks, and holes. The thief: inadequate ductwork. Ducts disperse air throughout houses with forced-air heating and cooling systems. However, leaks in your ductwork can cause your utility bill to go up and the money in your pocket to go down. If you have leaks in your ductwork, it is important that you know how to properly seal them.


The best product for duct sealing is duct mastic. Even commercial buildings rely on duct mastic to reduce air leaks in their large heating and cooling systems. Duct mastic is a malleable sealant that is capable of stretching as ducts expand and contract. Who doesn’t like something that can be flexible?

People commonly want to use duct tape, but duct tape has it’s own disadvantages. We recommend sticking with the duct mastic which can be found at your local hardware store.

Application Process

  1. Turn off your furnace before starting.
  2. Put the duct mastic on the areas you are working on.
  3. Spread it out.
  4. Let it dry.
  5. Don’t touch anything until you clean your hands.

For larger leaks:  When I say large, I mean ¼” or bigger. For these “big” guys, you’ll want to turn to mesh tape for reinforcement. This adhesive tape is made of fiberglass and is treated to trim down on smoke development. Mesh tape and duct mastic is an unbeatable duo, like two peas in a pod – or two sealants on a duct.

Duct Sealing Tips and Tricks

  • Wipe joint area clean to ensure a tight seal
  • Secure joints with screws, rivets, or other fasteners. It’s a must.
  • Make sure there is at least a ½’ overlap around any crack, hole, or joint.
  • UL 181-rated duct mastic is preferred because it is proven to be more flexible, adhere better, and last longer.
  • Both water-based and solvent-based are available types of duct mastic, however water-based produce less fumes.

Questions or comments? Be sure to leave a comment below!



4 thoughts on “How To Seal Ductwork”

  1. i thionk by this way you can secure your surroundings, because Duct Sealant is a high-speed setting, composite designed as a dual sealant for high speed air-conditioning ducts installed within homes. It may be used with or without reinforcing tapes. It has a soft “spread type” scent and applies plainly without stringing. Automatic systems are normally required to provide rigidity to the duct system. So be aware of this technology.

  2. I just wanna say that your website is very great. If you post more articles like these, I’ll follow your website to read more interesting stuff.

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