Duct Loss


Q.  What is Duct Loss?

A  1.  Duct loss is a common term used when performing load calculations on homes.  In this case duct loss refers to the thermal loss of Btu.s due to where the duct systerm is located and and how well insulated the duct system is.  Duct systems located in attic areas can experience a significant duct loss of 15 to 30 percent depending on how well insulated the ducts are and how well vented the attic is.  This type of duct loss, will require more expensive, larger capacity systems that will cost more to operate for the life of the system.  This type of duct loss is unavoidable with duct systems located outside the conditioned space of the house … but steps should be taken to minimize the duct loss.  The problem can be avoided all together by simply locating all ducting inside the conditioned space of the home.

A 2. Duct loss is also a common term used by Home Energy Raters in reference to conditioned air that leaks into and out of ducts systems.  Air leaking into or out of duct systems created pressure differentials between the air inside and outside a home.  These pressure differentials cause unconditioned and unfiltered air to infiltrate the home.  Conditioned air that leaks from a duct system into an unconditioned space must be replaced by unconditioned air entering the home.