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Seal Exposed Ductwork

Learn how to seal exposed ductwork in your furnace and air conditioner with these tips.

Sealing Ductwork.

Tools & Materials

Product costs, availability and item numbers may vary online or by market.

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Identifying Leaks

Ductwork is the system in which conditioned air is transported to heat or cool your house. In an average home, up to 20 percent of that air is lost due to leaks, holes and faulty connections. Look for tiny holes in the tubing, gaps and branching lines of dust and dirt at duct connections. Most problems are found at the duct joints, duct connections and where ducts meet an air vent or floor register.

Below are signs your ductwork may need attention:

  • High summer and winter utility bills
  • Rooms that are difficult to heat and cool
  • Stuffy rooms
  • Poor air quality, such as excessive dust



Ductwork can be hard to access. If you don't feel comfortable making repairs, contact a professional.

Before You Shop for Materials

  • Check to see how much of your ductwork is accessible from the basement, crawlspace or attic.
  • Check whether ducts are made from sheet metal, fiberglass, flexible tubing or a combination of these. Tape works especially well on fiberglass and flexible ducts as well as flat metal ducts; liquid duct sealant provides a tight seal around odd-shaped metal joints.

Wear eye protection when sealing ductwork. You’ll be working in dusty conditions and, in the case of sealant, brushing on liquids overhead. Wear disposable latex or nitrile gloves when using liquid sealant.

Tape Ductwork

Step 1

Vacuum ductwork where possible and wipe it clean with soapy water. Check for any loose fittings that can be tightened.

Step 2

Apply the foil HVAC tape centered on the exposed seams in the ductwork. Use pieces long enough to wrap around the duct at each joint.

Step 3

Press the tape in place using a plastic putty knife.

Good to Know

Use a foil-backed, UL-listed, tape with adhesive that resists heat damage and aging. Never use duct tape, it's not long lasting.

Use Duct Sealant

Step 1

Vacuum ductwork where possible and wipe it clean with soapy water. If you find any gaps greater than 1/4 inch, fasten the pieces together again before applying sealant, or cover the gap with flexible mesh tape.

Step 2

Beginning from the top or upper sides, brush sealant onto the ductwork over the joints. Coat the ductwork with bands about 2 inches wide and centered on the seams. Using the brush, work the sealant into the seam. Allow at least one day for the sealant to dry.


Make sure there's plenty of ventilation where you work. You can find solvent-based duct sealants, but a water-based product will give your nose and your house a break.

Benefits of Sealing Ductwork

Ensuring your ductwork is properly sealed can:

  • Save money on energy costs
  • Make room temperatures more comfortable
  • Improve indoor air quality
  • Protect the environment by using less energy