Hot air leaking out of our homes in winter and coming in during summer wastes more energy than most of us would ever imagine. Air leaks may account for 15 – 25% of the heat our furnaces generate in winter. An average unweatherized house in the United States loses as much air as it would if a good-sized window were left open year round. Some $13 billion worth of heating/cooling energy escapes through holes and cracks in residences. Where are these leaks in your home: floors, walls, ceilings (31%), ducts (15%), fireplace (14%), plumbing holes (13%), doors (11%), windows (10%) and fans, vents (4%).