How to Block Air From a Heat Duct


Air from heat ducts, used with forced air heating, can be blocked in places where the duct is leaking or hot air is not needed. One way in which you can easily block air from a heat duct is to seal the duct to prevent unnecessary air from escaping. Blocking or sealing heat ducts can be done by a professional or you can complete the project yourself. You can block air from a heat duct by first locating where the air is leaking from the duct.

Things You'll Need

  • Mastic sealant
  • Painters tape
  • Metal tape
  • Tin snips
  • Screwdriver
  • Silicone caulk
  • Caulking gun

Sealing Heat Ducts

  • Examine the heating ducts in your basement and attic and see if there is any air escaping through the duct work or if there are ducts that have become disconnected.

  • Reconnect any disconnected pipe and use a screwdriver to tighten the clamp on the duct, if there is one present. Alternatively, you can place mastic sealant around the outer edge of the duct and then reconnect it.

  • Mark the location of any air leaks with a piece of painters tape.

  • Cut a piece of metal tape large enough to cover the air leak in the duct with a pair of tin snips. You will not be able to rip metal tape like you can painters tape or masking tape.

  • Apply the piece of metal tape over the leak on the heat duct. Press down on the tape with your hand to make sure that the metal tape adheres correctly.

Sealing Duct Vents

  • Turn off a heat vent when the heating system is on to check and see if there is air leaking from around the vent. If you can feel air coming out from the vent when it is closed the vent is probably not sealed correctly.

  • Cut the end off of a tube of silicone caulk and place it in a caulking gun. Press the trigger to force the push plate up into the tube of caulk.

  • Run a bead of silicone caulk around the edge of the vent and smooth it out with your finger.

  • Wait at least 12 hours for the caulk to dry and test the vent again.

Tips & Warnings

  • Blocking and sealing air ducts can save money on your energy bills because heat will no longer be lost through leaks.
  • Duct tape should not be used to block or seal air leaks because the fix will only be temporary.

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