Homes burn through a mortifying 21% of the energy used in the United States. A lot of that energy is spent heating and cooling your house. And even worse, a whole lot of that energy is spent heating and cooling your backyard and front porch, through leaks and holes in your building envelope.
Although some of the air leaks in your home are visible to the untrained eye — around old and untreated doors and windows, for example — much of the average home's air leakage takes place in areas you don't see. Much of it takes place because of something called the stack effect, or chimney effect, which works like this: in the Winter warm air works its way into your attic through structural defects, holes in your ceiling, recessed lighting, leaky duct work, the furnace flue, the plumbing stack, or a poorly sealed attic floor. As it does, cold air is drawn into infiltrates your basement or lowerst level through leaks and cracks in the foundation and walls. this is often the cause for lower levels being much cooler in the Winter-more than that casued by natural heat rise. Also it is often times a casue of feeling a draft by a window on the lower level. A home performance contractor doing air sealing work in your home will generally focus on air sealing the basement and the attic floor in order to minimize the stack effect, and thus minimize unwanted air movement throughout your home.
Perhaps equally important, air sealing is crucial for maximizing the performance of insulation, the other major component of your home's building envelope. The R-Value of insulation is determined under the assumption that there will be no air infiltration throughout the insulation — it assumes that there will be adequate air sealing around the insulation. Once insulation is left exposed to air movement (air moving up through your attic floor, for example), R-Value decreases.
Air sealing is an investment in your home that will actually put money back into your pocket month after month. When was the last time that happened with a home improvement such as new carpeting or granite countertops?