Window manufacturing has come a long way in the past decade. New glass coatings have allowed for homes to be more efficient than ever before. In fact, it's one of the top remodeling projects for American homes. The new low-e coatings improve energy performance. By adding extra layers of glass and increasing the thickness of airspace between the layers of glass, you reduce the heat transfer through windows and limit the amount of radiant energy emitted. Low-emissivity coatings actually were developed in the 80s, so many homes already feature some of what the new low-e coatings are doing.
The first low-e coating windows windows were revolutionary. The initial work was actually funded by the U.S. Department of Energy, which demonstrates just how important the attention to environmental protection and green energy should be. Still, the earliest work on low-e coatings started with help from a leading American university, known as MIT.
So how do low-e coatings work? It's thought that glass just reflects heat, but that's not really true with low-e coating windows. Actually, these type of windows slow down the emission of radiant energy. Basically, solar energy flows in through a window, absorbed by the floor or wall in the house, thus warming the surface, then it starts to radiate its own energy. That energy being radiated in the floor or wall is a long-wavelength electromagnetic radiation. With low-e coating, the glass inside or the suspended film will actually absorb the heat radiation and low-e coating will limit the emission of that energy, which goes back to the name for the coating, low-emissivity.
The production of these coatings led to the commercials for "Heat Mirror" in 1981, which doubled the R-value of a window from R-2 to R-4, and along with it, a new age of energy conscious window technology. Other companies also sought to place low-e coatings directly onto glass. These continued to grow in popularity and now dominate the industry, and directly coated low-e glass is one of the most popular types of windows today.
So where should you install these type of windows in your home? The most effective climates will allow the low-e coatings to block heat loss but also give you solar gain. Thus low-e coating should be on the outer surface of the inner pane of glass. This is known as the #3 surface in window terminology. In warmer climates, where you're more concerned with keeping unwanted heat out, the preferred location for the low-e coating is the #2 surface, which is the inner face of the outer pane of glass. There are also two types of coatings to remember: low coat and hard coat. Soft-coat low-e is a thin layer of silver deposited onto the glass through a sputtering process after the glass has been manufactured. Hard-coat low-e is a layer of indium tin oxide applied to the glass while still molten and just beginning to harden in the float-glass where it is produced.
If you do plan on shopping for windows soon, it would be a good idea to talk to your home improvement associate at the store about the different window coatings and see which one has the most innovative solar energy and radiation absorbency. There are a lot of new windows and coatings that also have low-e along with other innovations that will give your home even better control of its temperature and heat loss.