How Duct Leaks Can Affect House Pressures

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Depressurized House

Cross-section of a depressurized house. Four arrows indicate location of leaks.
  1. Supply ducts leak air outside living space
  2. Return takes more air from house than leaky supply ducts replace
  3. House is depressurized
  4. Air leaks in through holes in house air barrier

Pressurized House

Cross-section of a pressurized house. Four arrows indicate location of leaks.
  1. Return duct leaks take air from basement instead of house
  2. Supply ducts add more air to the house than leaky return ducts remove
  3. House is pressurized
  4. Air leaks out through holes in house air barrier

Excerpted with permission from No-Regrets Remodeling by Home Energy (1997)