Instructions for Using Aluminum Tape on a Furnace Duct


Aluminum tape, or foil tape, is used to seal ductwork, as opposed to duct tape, which is used for everything but sealing ductwork. The importance of properly sealing ductwork cannot be overstated. Research by Owens Corning has shown that unsealed joints in ductwork are the most significant factor in heat loss, with unsealed ducts having leakage rates of up to 24 percent. Fortunately you can seal your exposed ductwork yourself using foil tape. Seal all the seams in your ducts, including the longitudinal seams on round ducts and the corners of rectangular ducts.

Things You'll Need

  • Rag
  • Window cleaner
  • Foil tape
  • Scissors (optional)
  • Clean the area you are sealing with a rag and window cleaner. Dust that collects on the top of ductwork prevents the foil tape from adhering. Use any cleaning product that doesn't leave a residue; window cleaner works well because it dries quickly.

  • Cut or tear off a length of foil tape long enough to seal the seam. It's okay to use several pieces; overlap your joints by two or three inches.

  • Peel the paper backing off the foil tape, exposing the adhesive. Cover the seam in the ductwork. Press the tape in place with your fingers, flattening any wrinkles in the tape.

Tips & Warnings

  • For maximum energy savings, insulate ductwork in attics and crawlspaces after sealing.
  • Inspect all exposed ductwork, and repair any loose or broken joints before sealing.
  • Seal return air ducts as well as supply ducts.
  • Use caulking or urethane foam to seal register boots to the subfloor.

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  • Photo Credit air conditioner, conditioning image by Greg Pickens from
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