By Brian Clark Howard
In severe weather, these windows lose heat 10 times faster than the walls of your home. Low-emittance (low-E) coatings help restrict this transfer of heat, especially when applied to windows with two or three panes of glass. Low-E coatings are microscopically thin layers of silver or tin oxide that reflect up to 70% of infrared radiation (the energy that turns into heat inside your home) but allow visible light to pass through unhindered. This helps lower the U-value (thermal conductivity value) of your window, which means it has greater insulating power. As an added bonus, low-E coatings can also reflect ultraviolet light, preventing your furnishings from fading up to 75%. When window-shopping
, keep in mind that low-E coatings are not one-size-fits-all. They can be engineered for different functions: Coatings with high solar heat gain reduce heat loss from the inside and maximize the amount of heat transferred from the outside, a desirable quality in cold climates. Those with low solar heat gain reduce heat loss in winter, but also reduce heat gain in summer. So if you live in a warm climate your, a/c does not have to work as hard. And then there are spectrally selective low-E coatings, which are designed to admit a higher portion of visible light. Windows with low-E coating may cost 10-15% more, but should reduce heat loss by about 25% over plain insulated glass, which means they will pay for themselves in 5-10 years.