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Knowing What Makes Windows Energy Efficient Can Save You Money

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When it comes to increasing energy efficiency in your home, it’s easy to overlook the impact your windows have on your energy costs. Drafty windows are easy to identify, but you don’t have to have a noticeable problem with your windows to benefit from replacement windows. The correct windows can help you save costs when it comes to heating and cooling your home.

Thanks to advanced technologies, the glass in your windows can boost energy efficiency. And that doesn’t just mean tinting your windows. Multiple-pane alternatives, various types of glazing, gas fills and even the method used to install the glass can help you save money on your energy bills throughout the year, regardless of the weather.

Get to Know the ENERGY STAR® Basics
When choosing windows for energy efficiency, it's important to first consider their energy-performance ratings in relation to the Tucson climate and your home's design. What does “energy efficiency” even mean and how can you weigh the energy savings of one window against another once they’re installed?

ENERGY STAR is the government organization that provides consumers with a dependable source for energy efficiency information about products. When buying an energy-efficient window, look at the ENERGY STAR label. It will list a number of the factors that go into classifying performance. Here’s a breakdown of what these categories mean:

  • U-Factor: The rate of heat loss to the outside. A low U-factor is better.
  • Solar Heat Gain Coefficient (SHGC): Most commonly shown as a fraction, this is the amount of solar radiation that a window lets in. SHGC is measured on a scale from 0 to 1. Window SHGC usually ranges from 0.25 to 0.80. Again, a low number is better.
  • Air Leakage (AL): The rate at which air passes through the joints in the window. The lower the AL value, the less air leakage.
  • Visible Transmittance (VT): The amount of light the window lets through measured on a scale of 0 to 1, with values generally ranging from 0.20 to 0.80. The higher the VT, the more light you see.
  • Condensation Resistance Factor (CRF): How tightly the window resists water buildup on a scale from 0 to 100. The higher the CRF, the better the window will withstand condensation.

Make sure to look for scores based on whole-unit numbers as opposed to center-of-glass numbers (COG). Whole-unit numbers are more dependable indicators of the window’s overall performance, while COG may not be as consistently reliable in areas of the window farther away from the center.

More Panes, Less Pain
Energy efficiency is greater in windows with more panes of glass in them. Double-pane windows are a notable choice for homeowners looking to improve energy efficiency with replacement windows.

While they can cost more, triple-pane windows can offer an even better energy efficiency that is worth the investment. Adding a middle pane means increased protection against the elements and allows the inner pane of the window to stay closer to room temperature. A third pane also reduces any convection currents and drafts that could make a room colder.

Beyond improving energy efficiency, triple-pane windows also provide greater protection against sound and break-in damage than double-paned replacement windows. So, if you have noisy neighbors or live on a heavy traffic street, you might benefit from triple-pane windows.

More Than Just Tinting
The glazing on your window can make a big change in reducing both the SHGC and VT that influences ENERGY STAR ratings. For years, people have used tinted glazing to block sunlight and reduce glare. Two other options can help on both sides of the glass and increase energy efficiency in your home.

On windows with two or more panes of glass, insulated glazing is created when the glass panes are spaced apart and hermetically sealed, leaving an insulating air space. Insulated window glazing primarily lowers the U-factor, but it also improves the SHGC.

Low-e coating can also have an influence on energy efficiency. A microscopically thin, almost invisible metal or metallic oxide layer added directly on the surface of one or more of the panes of glass, low-e coating helps decrease the window’s U-factor and can reduce energy loss by as much as 30 to 50 percent.

Insulating with Gas
Increasingly common in modern homes, gas-filled windows are made of at least two panes of glass with either argon or krypton gas filling the space between panes. This gas creates another invisible barrier against the heat and cold that would influence a window’s U-factor or leakage rate.

Argon and krypton are safe, naturally-occurring gasses found in the air we breathe. Factory-sealing the gas between the window’s glazing layers reduces the possibility of leakage or condensation buildup on the interior and exterior of your windows.

Edge Spacers Seal Out Leaks
The last factor that helps improve your window’s energy efficiency is the edge spacer. Edge spacers serve a variety of functions. They:

  • Hold against the stress the window faces with expansion and contraction during times of heat and cold.
  • Provide a moisture barrier to prevent water or vapor condensation.
  • Provide a gas-tight seal that prevents the loss of any gas in low-e windows.

Windows are available in single-seal or double-seal systems. Aluminum seals are most common thanks to the material’s strong energy-conducting traits.

Single-seal systems include an organic sealant applied behind the spacers that holds the unit together and prevents moisture leakage. A double-seal system adds a secondary backing sealant, often silicon, to further defend against leaks. Double-seal systems are most often used in low-e windows to make certain to hold any of the sealed gasses from escaping.

There’s a lot of science that goes into developing an energy-efficient replacement window. But, by understanding the basics of what goes into the ENERGY STAR rating and understanding the differences in window glass options, you can buy windows that will make your home temperate and save you money at the same time.

Find out more about energy efficiency in your windows by visiting our professionals at Pella of Tucson. Call 520-428-0648 or stop by our showroom. You can also schedule an appointment online for a free, in-home consultation.

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