Where Should You Put Energy Efficient Windows In A Home?

Where should you put energy efficient windows in a home? If you are building a new house, then obviously you have some control over the placement of energy efficient windows and you can use this to your benefit.

If you are building a new house you will have more control over the placement of windows. In an existing house, there is not as much control. But it always holds true that south-facing windows offer the most energy benefits to your home whether they are energy efficient windows or not. This is especially true in colder climates that benefit from the warming rays of the sun on the glass of the windows. Energy efficient windows amplify this affect by using low emittance, or low-E, coatings of metal on the outside surface of the windows. These coatings also reflect the sun during the summer months, therefore acting as a shield from overheating.

Steven Poitz of Thermotech in Canada says, "Often we suggest different glazing options and different glass combinations for different sides of the house. On the north we normally would use a more highly insulating window where there is less solar gain, especially in the winter time when you need the solar gain. There is a formula that is very good at blocking the free heat from the sun, and this is good for the larger window(s) facing west. Windows can get a lot of overheating from the west because the sun is very low in the sky by the time it sets to the west. You cannot use an overhang to block overheating from the afternoon sun because the sun is so low and the overhang would have to be quite long. So this would be an appropriate place to use low-E glass that blocks out the free heat from the sun. On the north windows it is okay to have the kind of low-E coating that lets the heat in. It will not add to your air conditioning bill. East and west, however, have really different microclimates with respect to the sun. So there is a different sun management philosophy for each of the different orientations, which includes shading, but that is another issue."

Poitz goes on to explain how the heat from the sun affects windows and the temperature of your home in order to better help us understand why these energy efficient windows work the way they do.

"The radiation we get from the sun is classically divided into three different types. The shortest wavelength, the bounciest and the highest energy, is ultraviolet, which you cannot see because it is beyond the purple spectrum. Then there is visible light, which goes from violet to red, and then there is what we receive, which is past red, but it is not visible light, so it is called infrared. Infrared is the part that most low-energy glass blocks out. It is similar to turning on an electric stove element. When you put your hand over it and it's warm, but it is not red yet. That is the kind of heat that low-E glass would block. However, if you live in a northern climate you would want the other type of low-E glass, the one that lets in the solar infrared. It does not just let in the light; low-E glass also lets in the heat from the sun. The south-facing windows let in more energy because the sun tends to be lower in the sky in the winter and the sun comes in more directly. In the summer time, the sun is higher in the sky, especially if you go further north. Most people do not realize that a south-facing window gets a lot of heat through it in the summer time, but not much more than a north-facing window."

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