Several research studies have taken a close and practical look at duct systems in homes. The results are astounding. They show duct leakage and location of supply and return outlets have a much greater impact on overall home energy usage than previously thought.
The magnitude of the observed leakage from an uninsulated system when the air handling unit is turned on may double or triple the home infiltration rate and increase space conditioning costs by an estimated 10% to 12%.
With field data from well over 1000 houses in different regions of the country, these tests demonstrate that duct leakage is a major cause of energy loss. Pressure imbalances in the house produced by leakage, duct location and forced air distribution systems, can also cause secondary problems such as increased radon and moisture entry through foundations, plus possible back drafting of combustion appliances.