Every inch of duct work in the attic will get warm when it is not on. As the unit comes on it will push the stagnated air out of the lines and then bring along the cooler air. No amount of insulation can prevent this. The same is true for heating in the winter. Some newer units i.e. American Standard have a continuous variable speed motor that keeps the lines at a consistant temp.

Edited by ElectriDon - 23 Aug 2007 at 6:45pm