Your window is only as good as the glass in it, Experts estimate that 70 percent of infrared energy is absorbed through windows and doors, and 90 percent of the heat absorbed occurs through the glass. With more people becoming more environmental conscious today energy efficient windows are being sought out more than ever, but from my experience with everyday customers there is misinformation being thrown around ,my goal is to clear some the air of some of that misinformation so that you can have a realistic and an overall understanding of what Low-E is and does.
What is Low-E? Low-E stands for Low Emissivity, Emissivity is the measure of an objects ability to release or absorb Infrared energy. Infrared radiation is not visible to the human eye, but we feel it as heat. Low-E
is a thin micro coat that is thinner than human hair, it is placed on the inner part of the outside window pane in a double pane impact glass, this is called solar control Low-E, this is used in warmer climate areas, the Low-E that is used in colder weather is called Passive Low-E. Low-E simply put works by allowing solar light into your home by bouncing Infrared energy or heat back outside, thus making it easier on your AC unit to keep your home cool.
Are Impact windows considered energy efficient? Not exactly, impact windows are more energy efficient than standard non impact glass, but they do not hold the capabilities that a glass treated with Low-E has. The most important measurement when looking at the energy efficiency performance that a window has is the solar heat gain coefficient or SHGC. When shopping for an energy efficient window a SHGC of .30 or less is what you should typically aim for, you will only achieve that mark with a Low-E glass or insulated glass. To give you an idea of how well low-e performs in the energy efficiency area, window with a 5/16 glass thickness with a clear glass has a .64 SHGC and a non impact window's are around the .70's, a Low-E glass is usually under .30.
In conclusion Low-E films are great at what they are intended to do, and that's keeping heat out of your home. Some things to keep in mind is that low-e films give a slight greenish-reflective appearance, in my opinion it gives the glass a modern-ish look and it pairs really well with white frames. Low-E glass also increase the price per unit, but if you weigh in what you can potentially save on your overall home energy, they are well worth the money. When buying impact windows I recommend people to ask for the thermal reports for the windows and doors that they are planning to purchase, depending on the window and door manufacturer the SHGC can vary.