It must be hard for a consumer to decide how to select replacement windows or windows for a new home.  How do you start, where do you start and who do you trust for such an important investment?  All the manufacturers claim high efficiency glass, tax incentives and new and improved technologies.  In my career at Natelli Homes, which is going on 25 years in residential construction, the window and door industry has grown and improved the most.  The standards for all the major manufacturers are so much improved that I would venture to state that there are arguable financial and performance benefits to replacing windows that are only 10 years old.

Windows and exterior doors are the biggest contributors to heat and energy loss in a home.  People notice it more in the winter when we can feel the cold spots and drafts around windows and doors, but imagine how much is also lost in the summer when we are not quite as sensitive.  Poor performing windows and exterior doors contribute to an immeasurable amount of energy loss in our world.

Again, where does one start?  You might start with the U-value of a window which is a measurement of 4 combined ways windows lose heat.  This is a standard by which a homeowner can evaluate the performance of manufacturers on an even playing field.  Simply put, the U-value of a window combines the heat loss of a window through (1) radiation, (2) convection, (3) air leakage and (4) conduction.  The lower the U-value the better performing the window is.

I found a great sketch in an article by Paul Fisette in Fine Homebuilding.  Paul Fisette is director of the Building Materials Technology and Management Program at the University of Massachusetts in Amherst, MA (www.umass.edu/bmatwt). Chart information courtesy of W. W. Norton & Co. Inc., except where noted. Photo: Brian Vanden Brink; drawings: Dan Thornton.