Window Thermal Performance According To Geography

Posted on Friday, November 25th, 2011

Have you ever had a hot drink in a glass? If you have, you probably learned a lesson. If you haven’t, I wouldn’t recommend giving it a try, but even common sense tells us that it is probably going to be really hot. That’s why some glass manufacturers have created double walled glasses, so you can still see the color of your drink, without being affected by the temperature. Also, whatever liquid is within the cup will hold its temperature for a longer period of time.

Single-pane windows are just like the drinking glass. Dual-paned windows cut down on the flow of heat. And if you inject an inert gas like argon or krypton, there will be even less heat transfer. It’s like adding clear insulation between the glass.

A window’s thermal performance is measured in three spots: the center of the glass, the edge of the glass (often the coldest point), and the frame (the warmest point). The average of these three numbers is known as a windows U-factor, its overall ability to resist heat flow.

Different Windows For Different Geographies

When there is a difference between inside and outside temperatures, heat transfers through a window. Sometimes, the transfer is welcomed. In a cold climate, the sun’s heat and light improve the efficiency of the home since it reduces heating costs. In a warm climate, we don’t want the heat, but we do want the light. Fortunately, advances in window technology let us have it both ways.

Less than half of the sun’s energy is visible. Longer wavelengths, beyond the red part of the visible spectrum, are infrared, which is felt as heat. Shorter wavelengths, beyond purple, are ultraviolet (UV). When the sun’s energy strikes a window, visible light, heat and UV are either reflected, can be either absorbed or transmitted into the interior. Visible light is always welcome, the more the merrier. UV is blocked to protect you interior so that the colors don’t fade.

Depending on your geography, you might want to let the heat in through the windows for better warming efficiency, but in the South, home’s are better off blocking it for better cooling efficiency. Give us a call, or consult The Efficient Windows Collaboration to find out what windows are the best for your home’s unique needs.

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