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The Science Behind Energy Efficient Windows

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Energy ratings for windows take the guesswork out of window shopping. It also helps to understand the science of how different materials and constructions are used to make energy efficient windows. There are a lot of windows out there claiming to be eco-friendly and efficient, so how do you compare?

The main rating to check is U-factor. This tells you how well the window prevents heating or air conditioning from escaping, and outdoor temperatures from coming inside. The lower the U-factor, the better.

Another rating is the solar heat gain coefficient (SHGC). This indicates how well the glass blocks the sun’s heat from entering the home. Look for low SHGC numbers for windows that face the sun in rooms with high A/C needs. If you have a room that needs solar heat to stay warm in winter, a higher SHGC may be better.

Now let’s find out why double glazing and low-e coatings are best for energy efficient windows.

Gas-Filled Double Glazing

Double glazed windows protect against heat transfer, similarly to how a restaurant can use double entry doors to help keep heating and air conditioning inside. Between the two panes of gas, dead air traps the heat from moving in either direction.

Why it works: certain elements are better at trapping heat. Think of a chemistry lesson where you learned about atoms moving quickly or slowly. This movement of atoms affects how well a particular gas conducts heat. When the goal is energy efficient windows, you want slow-moving gas filling the gap between the double glazing.

Energy efficient windows use argon, krypton, or a combination of gas fills. Pure krypton gas performs best, so if your budget allows, choose krypton! Argon is most common, though. It costs less and lets about 1/3 less heat transfer compared to regular air.

Low-E Coatings

Energy efficient windows can use low-emissivity coatings like a reflective shade for your car’s windowshield — except you want natural light to come pouring in. Low-e coatings reflect away the sun’s rays that heat up a home’s interior, while letting in visible light.

Why it works: sunlight includes a spectrum of wavelengths. The goal of low-e coating is to block certain wavelengths of light from passing through the glass. Infrared light heats up the home. It also has longer wavelengths than visible light. So, low-e coatings should block as much infrared light as possible.

Silver or other materials that reflect infrared light are used to make energy efficient windows. The coating gets applied while the glass is being made, or after it’s cooled in a lamination method. The laminated kind, solar control coating, works a little better but any high-quality low-e coating is good for energy efficient windows.

About Air Leakage

Installation quality and window choice are important — you don’t want a leak undermining the performance of your energy efficient windows!

The science is simpler when it comes to air leakage: you need a tight seal around the frame and an opening mechanism that seals off properly when closed. Consider adding some casement or awning windows that open easily for ventilation and seal tightly when closed.

Upgrading to more energy efficient windows? Contact us at danddglassworks.com as we can help you find the best options for every size, shape, and location. Learn more today about energy efficient replacement windows in the north San Francisco area!

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