One of my Aunts sent me a link to a great website called "Efficient Windows Collaborative" that has a wealth of information about different types of energy efficient windows, and a guide to help you find the right type of window for your particular area of the country! I had no idea it was this complicated.

First we have to choose between single, double or triple glazed windows - glazing is the number of layers of glass in the window. Triple glazed are recommended for places where the winters are cold and the summers are hot - I'm thinking of a house in Kansas with no trees to block the wind or provide shade in summer. As mentioned in an earlier post, our house has several mature trees around it, plus we have deep eaves, so there are only a few windows that get direct sun in the summer, and thus we rarely need an air conditioner, even when it is 90 degrees out.

The picture shows a double glazed window.

Single glazed are what we have now, although there are some types of glazing that add a tint to reduct heat and light transmission through the glass. These windows don't provide the energy efficiency that we are looking for, so we are opting for double glazed (sounds kind of like a donut - yum!)

There are actually several types of double glazed windows available: first, we need to decide the "solar gain" level we want. There are windows rated low, moderate & high for solar gain. The term "solar gain" refers to the amount of solar heat that the window transmits to the inside when the sun is shining on the window. From the reading I did, this is a bigger factor in areas of the south where the sun shines a lot, and it rarely gets cold. In these places, by reducing the heat transfer through windows, you can really cut down on you air conditioning bill, so opting for a low solar gain window in those areas can make a big difference in energy use.

In our area, given our low A/C use and cold winters, we would rather have a moderate solar gain type of glazing - something that still allows a reasonable amount of solar heat to transfer in the winter, but does block some in the summer.

Then there is the "low-E" coating. E stands for emittance in this case, and low-E refers to a special coating that helps reduce heat transfer from one glazing layer to the next (in the case of double glazed windows). From what I could tell, this is standard if you opt for an energy efficient window. Simliarly, argon, krypton or argon/krypton gas filling the space between the glazing layers is also pretty standard once you get beyond tinted windows and into the highly efficient ones. The gases are just one more way to reduce heat transfer between the glazing layers -- this helps keep heat inside during the winter, and keep it outside during the summer!