A Guide to Window Efficiency Ratings

There are a lot of industry-specific terms when it comes to home products like insulation, doors, and windows. Unless you understand the meaning of these terms, it’s hard to figure out just how efficient or inefficient products may be. Probably the two most common measures of efficiency you will see when shopping for replacement windows are the “R-value” and the “U-value.” R-Value: The R-value index refers to thermal resistance and insulation against heat transfer. In the case of a home, this could mean keeping inside heat in or outside heat out. R-value is used as a way to calculate the rate at which heat is transferred between spaces. With replacement windows, this transfer is between the interior of your home and the outdoors. A higher R-value in a material like glass means that heat will be lost at a slower rate—the higher the number, the better for you and your energy consumption.

U-Value: The U-value is the reverse of the R-value and measures how well a material conducts or transfers heat. In the same way that a high R-value is good for your home, a low U-value is preferred, indicating a material’s ability to block heat transfer.

Low-E: A popular type of glass for energy efficiency is “Low-E” glass. The “E” stands for “emissivity,” specifically thermal emissivity. With Low-E glass, special coatings are applied which reflect infrared light (heat) but let visible light pass through. This keeps the heat on whichever side of the window it originated from and acts as insulation.

Examples of R-Value in Windows: A normal pane of glass will absorb some amount of heat, but not much. In fact, untreated glass has an R-value of about 0.85, which is less than wood. However, if you have insulated glass, your R-value jumps to 2.08. A soft coat Low-E insulated glass with argon has an R-value of 4.35.

At Wallside Windows, we’re proud to offer replacement windows that are highly energy efficient. Upgrading to replacement windows can keep your home warmer during cold Michigan winters and cooler in the summer. To read more about our replacement windows and how you can save energy at home, visit our website or call us at 313-292-4400.