Insulated Windows Go Both Ways
A surprise to many people is that Low E windows, the marvels that have made the old glass energy drain a mere shadow of its former self, are a two-way street. They can keep heat in, or they can keep it out! And when planning a window scheme, it's an important thing to know.
Low E windows (the "E" stands for emissivity), have been coated with a thin coat of metal or metallic oxide. The coating blocks much of the ultraviolet light that damages fabrics and floors. It also blocks long-wave infrared light, responsible for heating. Depending on how the window is constructed, it can block the heat from entering the building or block it from escaping. While the Low E coating [http://www.doorandwindow.com/windows/glass-glazing-treatment/] blocks the invisible light from both ends of the spectrum, it allows almost all the visible light that we can see to pass through the glass.
For example, in a cold climate, you want the heat from the sun. By putting the coating on the inside of the outer pane of glass in your double-pane window, the infrared (heat) that comes off surfaces hit by the sun is reflected off the coating and back into the house. This "solar gain" works wonders for heating--it is reported that the outer pane of glass in well-made Low E windows can be 20 degrees and the inner surface of the window will be 65 degrees. If the window were single pane, the inner temperature would be a frigid 30 degrees.
Of course, the high solar-gain window is an anathema in a hot climate where air conditioners rule. Who wants to keep more heat in the house when your AC already is working overtime to keep you cool?
The answer is low-solar-gain Low-e windows. Put a slightly different coating on the window and the infrared radiation is blocked from entering the house completely, thus removing the heating effect of the sun. How cool is that!
And windows also are designed to work both ways (though they are less efficient) for in-between heating situations.
Now the real trick comes where you are planning a window scheme for your house where you have a very sunny side with lots of glass that is going to cook you much of the year, and a shady side that can use the solar heat. The answer is to mix and match your windows. This is where you probably want a window expert who best knows the ratios of varying Low E glass and what will work best for your specific solar situation.
But isn't it great to know that when it comes to Low E windows, you can have it both ways?
Low E windows (the "E" stands for emissivity), have been coated with a thin coat of metal or metallic oxide. The coating blocks much of the ultraviolet light that damages fabrics and floors. It also blocks long-wave infrared light, responsible for heating. Depending on how the window is constructed, it can block the heat from entering the building or block it from escaping. While the Low E coating [http://www.doorandwindow.com/windows/glass-glazing-treatment/] blocks the invisible light from both ends of the spectrum, it allows almost all the visible light that we can see to pass through the glass.
For example, in a cold climate, you want the heat from the sun. By putting the coating on the inside of the outer pane of glass in your double-pane window, the infrared (heat) that comes off surfaces hit by the sun is reflected off the coating and back into the house. This "solar gain" works wonders for heating--it is reported that the outer pane of glass in well-made Low E windows can be 20 degrees and the inner surface of the window will be 65 degrees. If the window were single pane, the inner temperature would be a frigid 30 degrees.
Of course, the high solar-gain window is an anathema in a hot climate where air conditioners rule. Who wants to keep more heat in the house when your AC already is working overtime to keep you cool?
The answer is low-solar-gain Low-e windows. Put a slightly different coating on the window and the infrared radiation is blocked from entering the house completely, thus removing the heating effect of the sun. How cool is that!
And windows also are designed to work both ways (though they are less efficient) for in-between heating situations.
Now the real trick comes where you are planning a window scheme for your house where you have a very sunny side with lots of glass that is going to cook you much of the year, and a shady side that can use the solar heat. The answer is to mix and match your windows. This is where you probably want a window expert who best knows the ratios of varying Low E glass and what will work best for your specific solar situation.
But isn't it great to know that when it comes to Low E windows, you can have it both ways?
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