Energy Efficient Windows – Solar Heat Gain and U-Factor

    Published: 06-16-2009
    Views: 14,948
    In this video, Andersen Windows’ Brian Gunderson talks about the numbers behind energy efficient windows. Numbers can get confusing. Here you’ll learn about rating systems for windows and doors and what you should look for when choosing energy efficient window and door products.

    Brian Gunderson: Hi! I am Brian Gunderson with Anderson Windows. I am here to talk to you today about energy efficient windows. Numbers can be confusing. Today, we'll talk about the rating systems for windows and patio doors and what you should for when choosing an energy efficient window product. If you are in the market for windows you've probably heard of some terms regarding energy performance like U-Factor, Solar Heat Gain Coefficient and Visible Light Transmission or VT. Energy saving features are a great way to add sustainability to your home and your lifestyle. But what do all the numbers really mean about window performance? I am going to help you understand these numbers so you can make the best and the right choices for how and where you live? U-factor is a measure of how well your window prevents heat from passing through it.

    This is particularly helpful when the temperature difference outside to inside is extreme. The lower the U factor compared to other windows, the better. The Solar Heat Gain Coefficient or SHGC tells you how well your window or patio door prevents solar energy from passing through it to the interior of your home. Again, lower is better here.

    In some climates or times during the year, you may benefit from solar heat well in others you may not. Believe it or not your windows can do both. Keep out solar heat in the hot summer months, when you are running the air conditioner as well as let some heat into your home in the cooler months when heating is necessary.

    Finally, Visible Light Transmission or VT measures how well the window allows visible light to pass through. Coding and films can help reduce the VT but most people want as much light into their space as possible. That's why you have a window to let light in. Higher is better with VT; it's telling you that the window lets more light into your space. Technologies exist now to maximize the visible light transmission while minimizing the heat gain and the effects of ultraviolet light. All these measures work together to determine the window and door performance. Third party organizations like the National Fenestration Rating Council or NFRC conduct tests on products to determine the rating for windows and patio doors.

    These numbers are included in the product labels for most windows. Windows are made of a lot of different materials and ratings show how they work together to provide the most energy efficient protection for your home. In addition, sustainability in the manufacturing process is becoming more and more important to consumers.

    The kinds of materials you use, where it comes from and what happens to factory waste determine just how sustainable the manufacturing process is? You may have heard of a term R value. It's actually the energy efficiency measure for a wall. For windows and patio doors the best measures are those that we've defined earlier U factor, Solar Heat Gain Coefficient and Visible Light Transmission. These measures apply more commonly to windows. So it gives you a better ability to compare one product to another. Talk to your contractor or a window expert in your area about the best choices for your geographical location. I hope this information helps you better understand the various energy efficient terms when selecting windows for replacement.