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In our last post, we explored the first and most fundamental step in window replacement: deciding on whether you will select wood or vinyl window frames. This decision is an important one, but it isn’t the only factor you’ll need to consider before moving ahead with your window replacement project. Read on for our best advice on next steps.

Navigating Home Window Replacement: Energy Efficiency Basics

Important Energy Efficiency Consumer Terms

Ensuring that your window replacement will yield energy savings is hugely important. In order to choose products that will lower your energy bill and keep your house protected from cold and hot weather, familiarize yourself with these two important terms:

  • U-factor: This term simply describes how well a window resists heat flow–in the summer, heat transfers from outside to inside. In the winter, vice-versa. A lower U-factor indicates a slower heat transfer–in other words, the lower the U-factor, the better the window is at insulating your home. Not every home is equal, though. The U-factor you should seek out depends on your geographical location. Use the US Department of Energy’s map and table to help you determine what U-factor is right for your home.
  • Solar Heat Gain Coefficient (SHGC): This term is different from the U-factor because it refers specifically to how much heat from the sun your windows allow into your indoor environment. As the USDOE explains, “The lower the SHGC, the less solar heat it transmits and the greater its shading ability. A product with a high SHGC rating is more effective at collecting solar heat during the winter. A product with a low SHGC rating is more effective at reducing cooling loads during the summer by blocking heat gain from the sun. Your home’s climate, orientation, and external shading will determine the optimal SHGC for a particular window, door, or skylight.” So, many factors beyond geography will influence the ideal SHGC for your windows. A competent contractor will be able to help you determine this.
Additional Energy Efficiency Options

Beyond choosing windows with the appropriate U-factor and SHGC value, there are some consumer options for you to consider to make your new windows even more energy-efficient. These options fall into three categories: glazing, glass fills, and coatings.

Window Glazing and Energy Efficiency

Insulated window glazing–that is, a product that features two panes with an air-filled space in between–is one of the most common ways to add additional insulating power to your windows. The air that exists between the two panes slows heat transfer, ensuring a more comfortable indoor environment. You can opt for three-pane, or triple-glazed, windows, further increasing your home’s insulating power.

Gas Fills and Energy Efficiency

Gas fills constitute another popular choice for upping your windows’ ability to keep the cold air out (or in). Double- or triple-glazed windows can be filled with one of two non-toxic gasses, argon or krypton, or a mixture, all of which slow the heat transfer considerably. These gasses are used because, in addition to slowing the transfer of heat better than regular air, they minimize the opportunity for moisture to condense inside the two panes of glass.

Low E-Coatings and Energy Efficiency

One additional layer of protection against heat transfer that is available to consumers, low-emissivity or “Low-E” coatings, can yield significant cost savings. As the US Department of Energy explains, “A Low-E coating is a microscopically thin, virtually invisible, metal or metallic oxide layer deposited directly on the surface of one or more of the panes of glass.” According to the agency, while these coatings tack on an additional 10-15% in costs, they can reduce energy loss by 30-50%! We’d say that is a pretty good return on investment, making Low-E coatings a popular choice for home window replacement.

All of these measures of energy efficiency will come with their own costs, of course, but the long-term investment in your home’s energy efficiency will be almost immediately noticeable in your energy bill. If you’re unsure of what direction to go in to make your home window replacement as energy efficient as possible, we are here to support you!

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