A respected builder I know told me how he learned the true value of energy-efficient windows. In the course of his business, he installed a builder's line of windows from a well-known manufacturer in every house he built. He felt good about his choice; he purchased the windows from a manufacturer with a reputation for quality, but they cost 10% less than the same manufacturer's standard line of low-E, argon-filled windows, saving him about $600 per house. He even put them in his own new home. The first winter he lived there, though, he noticed that the windows seemed cold. Only then did he compare the U-values with the same manufacturer's standard windows. He did some math and concluded that his windows were costing him about $150 a year. By his estimation, the low-E windows would have paid for themselves in four years and made his home more comfortable for their entire life span.
My friend based his conclusions on widely accepted averages, and although certainly not exact, they were probably not far off the mark. Experiences such as his are common, yet they are easily avoidable with a basic understanding of how energy-efficient windows work. When you choose new windows, appearance is often the first consideration. Initial cost is the next issue: Which window within the favored style costs the least? But liking a window's appearance is a fuzzy proposition, and cost really depends on durability and on the energy dollars pumped through the windows each year (see Annual heating costs). I am convinced that if we could see energy loss as we see color and shape, energy performance would top the list of window considerations.
Windows are thermal holes. An average home may lose 30% of its heat or air-conditioning energy through its windows. Energy-efficient windows save money each and every month. There are even some cases where new windows can be net energy gainers. The payback period for selecting energy-efficient units ranges from two years to ten years. In new construction, their higher initial cost can be offset because you'll probably need a smaller, less expensive heating and cooling system. And more-durable windows may cost less in the long haul because of lowered maintenance and replacement costs. Plus, you'll be more comfortable the whole while you live with them.