Ducts pressures that originate at the air handler pull outdoor air into buildings through leaky return ducts and blow conditioned air through holes in supply ducts. HVAC installers cut holes through the envelope to install ducts and these holes are often large envelope air leaks.

Furnaces and air conditioners create high pressure inside of ducts. That high pressure can pressurize buildings and increase envelope air leakage whenever the furnaces and air conditioners operate.

This lesson begins by discussing duct leakage standards. We then discuss these duct air sealing topics.

  • How to locate air leaks in different types of ducts.
  • How to test and repair leaky duct systems.
  • How to seal the duct air leaks permanently.
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