Cavallo J
Bibliographic info:
USA, Home Energy Magazine Online

More than three-fifths of the households in the U.S. heat or cool their homes with ducted forced air systems, so chances are good that air ducts are lurking within your walls, floors, or ceilings. These air ducts move conditioned air to warm and cool your family. They can be a great source of comfort-but more likely they are wasting energy and costing you money. Typical duct systems lose 25 to 40 percent of the heating or cooling energy put out by the central furnace, heat pump, or air conditioner. What that means is that it is likely that more than a quarter - and perhaps almost half - of the money you spend to heat and cool your home literally could be vanishing into thin air.