Let’s make this all about U.
If you could only look to one fact about a window before buying it, the most important fact you can look to in your window is its U factor. The U factor is the industry benchmark by which a window’s energy efficiency is measured. The U factor is the measurement of how fast energy (and heat is energy) is going to flow through a window. Each component of a window contributes to the U factor, and some components contribute more than others. So before drilling down in the details of the window, look at the window’s U factor first. OK, but what’s a good U factor? The lower the U factor, the less energy there is moving through the window. The current Energy Star Rating for windows in Chicago area is a U factor equal to or less than .30. But the Energy Star Ratings are expected to change in 2016, and it is expected that the new minimum standard for windows in Chicago will be a U factor of .27. So what is passing today as energy efficient this year will be sub par a year from now, which brings up an important point: The efficiency of the windows you buy will not get better with age. So prepare for tomorrow by getting the lowest U factor available within reason.