WINDOWS & DOORSGENERAL INFOWindows take up a proportionately small area of the thermal envelope, yet they are one of the most used parts of a home—for light, ventilation, passive heat, and aesthetics. Windows can represent significant heat loss in Alaska because of their low insulative value relative to other components of the building. Thus having an energy efficient, durable window (located in the right place) makes a big difference in your overall home energy performance.