When it comes to increasing energy efficiency in your home, it’s easy to forget the impact your windows have on your energy usage. Drafty windows are easy to recognize, but you don’t have to have a noticeable concern with your windows to benefit from replacement windows. The right windows can help you save money when it comes to heating and cooling your home.
Thanks to modern 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 all year long, regardless of the weather.
Get to Know the ENERGY STAR® Basics
When considering windows for energy efficiency, it's important to first consider their energy-performance ratings in relation to the South Portland climate and your home's design. What does “energy efficiency” even mean and how can you compare the energy savings of one window against another once they’re installed?
ENERGY STAR is the government group that provides consumers with a dependable source for energy efficiency information about products. When buying an energy-efficient window, read the ENERGY STAR label. It will show a number of the factors that go into identifying 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 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 strongly the window resists water buildup on a scale from 0 to 100. The higher the CRF, the better the window will guard against condensation.
Make sure to seek 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 may not be as consistently reliable in areas of the window farther away from the center.
More Panes, Less Pain
Energy efficiency is improved in windows with more panes of glass in them. Double-pane windows are an attractive choice for homeowners looking to improve energy efficiency with replacement windows.
While they can cost more, triple-pane windows can offer an even higher energy efficiency that is worth the investment. Adding a middle pane means more protection against the elements and allows the inner pane of the window to stay nearer to room temperature. A third pane also reduces any convection currents and drafts that could make a room chillier.
Beyond improving energy efficiency, triple-pane windows also offer greater protection against sound and break-in damage than double-paned replacement windows. So, if you have noisy neighbors or live on a crowded 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 impacts ENERGY STAR ratings. For years, people have used tinted glazing to absorb 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 predominantly lowers the U-factor, but it also improves the SHGC.
Low-e coating can also have an effect 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 today, gas-filled windows are made of at least two panes of glass with either argon or krypton gas filling the space between them. 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 benign, 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 resist water or vapor condensation.
- Provide a gas-tight defense 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 use an organic sealant applied behind the spacers that holds the unit together and restrains moisture leakage. A double-seal system features a secondary backing sealant, often silicon, to further defend against leaks. Double-seal systems are most often found in low-e windows to make certain to prevent any of the sealed gasses from escaping.
There’s a lot of science that goes into creating 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 find 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 professionals at Pella of South Portland. Call 207-517-2331 or stop by our showroom. You can also schedule an appointment online for a free, in-home consultation.