Defining U-Values and R-Values when Shopping for Replacement Windows October 21, 2014 Trying to understand all of the different terms and options that exist with regard to replacement windows can be confusing. Most people only have to shop for replacement windows or doors once in their lifetime. That’s because the average life expectancy of windows is about 15 to 20 years. Doors can last even longer, but that all depends on the use and abuse that they see. When you begin shopping for replacement windows, you’ll hear the term U-Value and R-Value. These are technical terms but they can have a direct impact on not only the type of windows you choose, but also in their energy efficiency. Living in Toronto, you want to make sure that you have highly energy efficient windows. The winters can be tough here and the colder it gets, the more you’ll want to protect your home and the heat your furnace produces. U-Value This number is essentially letting you know how much heat is going to escape through the window, either through the glass or the frame. The lower the U-Value, the more energy efficient that window is going to be, which means you’ll save more money over time with it. R-Value This number reflects the window’s resistance to heat flow. It’s kind of the opposite of U-Value, but a little different. The R-Value will depend on the layers of glass that the window consists of. The higher the R-Value, the more resistant it will be to heat flow, so the heat in your home will remain in your home longer and more efficiently. The goal should be to focus on windows that have low U-Values and high R-Values. This should help you narrow your focus on choose windows that are not only going to look great in your home, but that will actually help you save money on your heating expenses throughout the winter.