Roughly 40 percent of the unwanted heat that builds up in your home comes in through the windows. Replacement windows  are one of the smartest home improvements you can make to help drive down your heating and cooling costs  and keep conditioned air from escaping your home.
Since most energy efficient features can't be seen, it's important to know what to ask for when shopping for replacement windows. For starters, be sure to ask for double-pane windows with low-e glass, a special coating that reflects UV rays. The e stands for emissivity and that is what stands between your home and lots of UV radiation. This prevents sun damage to rugs, floors, window treatments and other furnishings, and will reduce the pain of high energy bills as well.