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Knowing What Makes Windows Energy Efficient Can Save You Money

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When it comes to improving energy efficiency in your home, it’s easy to overlook the impact your windows have on your energy usage. Drafty windows are easy to recognize, but you don’t need to have a noticeable problem with your windows to benefit from replacement windows. The proper 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 increase energy efficiency. And that doesn’t just mean tinting your windows. Multiple-pane choices, various types of glazing, gas fills, and even the method used to install the glass can help you save money on your energy bills all year long, regardless of the weather.

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

ENERGY STAR is a government-backed trademark that provides consumers with a trustworthy source for energy efficiency information about products. When buying an energy-efficient window, look for the ENERGY STAR label. It will list a number of the factors that go into identifying performance. Here’s a look at 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 indicated 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 normally 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 consistently 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 trustworthy indicators of the window’s overall performance, while COG numbers 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 for more energy efficiency with replacement windows.

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

Beyond improving energy efficiency, triple-pane windows also provide greater protection against loud noises and break-in damage than double-pane replacement windows. So, if you have rambunctious neighbors or live on a busy street, you might benefit from triple-pane windows.

More Than Just Tinting
The glazing on your window can make a big difference in reducing both the SHGC and VT that factors into ENERGY STAR ratings. For years, people have applied tinted glazing to block sunlight and reduce glare. Two other techniques 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 mostly 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 deposited directly on the surface of one or more of the panes of glass, low-e coating helps reduce the window’s U-factor and can lower 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 each one. This gas adds another invisible barrier against the heat and cold that would effect 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 final factor that helps improve your window’s energy efficiency is the edge spacer. Edge spacers serve a range of functions. They:

  • resist the stress the window faces with expansion and contraction during times of heat and cold.
  • serve as 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 because of the material’s strong energy-conducting traits.

Single-seal systems contain an organic sealant applied behind the spacers that holds the unit together and restrains moisture leakage. A double-seal system includes a secondary backing sealant, often silicon, to further defend against leaks. Double-seal systems are most often found in low-e windows to block any of the sealed gasses from escaping.

There’s a lot of science that goes into making an energy-efficient replacement window. But, by knowing 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 cozy and save you money at the same time.

Discover more about energy efficiency in your windows by chatting with our experts at Pella of Shrewsbury. Call (508) 925-7149 or stop by our showroom. You can also schedule an appointment online for a free, in-home consultation.