Taken individually, they may appear harmless. However collectively, the air leaks in your home could be compromising your indoor air comfort and increasing your monthly energy bills by as much as 25 percent. Many of these leaks occur around a home's “envelope,” or the roof, attic, subfloor, exterior doors, windows and exterior walls. “If you added up all the leaks, holes and gaps in a typical home's envelope, it would be the equivalent of having a window open every day of the year,” the U.S. Department of Energy says.