When you go shopping for windows, you are going to quickly discover that there is an entire world of window terminology that you are going to need to be familiar with if you want to be able to compare the different windows that you see and make the best buying choice possible. Here are 4 terms you should be familiar with.


A window's R-value is a measurement of how well the window is able to resist the flow of heat. The window is tested to see how much heat flows from outside of your home to the inside of it. When looking at the R-value of a window, the higher the number, the better. A higher number means that the window is more energy efficient.


A window's U-factor measures the opposite principle of the R-value. The U-factor is a measurement of how much heat passes from the inside of your home to the outside. In other words, it measures how much heat is lost from your home through the window. With the U-factor, you are looking for the lowest number possible in order to get the highest possible energy savings.

Low-E glass

Low-e stands for low-emissivity. Low-e is not a measurement; it is a type of coating that can be applied to windows. A low-e coating is a very thin metallic coat that you can't see with the naked eye. This thin metallic coat is placed on the inside of the window and is designed to reflect the heat from your home back inside. This coating will help ensure that the energy you spend heating your home in the winter isn't lost through your widows. This feature also helps keep your home cool in the summer as well.

Low-e coating serves another purpose as well. It also helps block ultraviolet rays from getting into your home. These are the types of sun rays that damage your skin and cause your belongings to fade.

Energy Star Ratings

All types of building materials and appliances can earn Energy Star ratings. Energy Star ratings are issued by an organization that is independent from all of the manufacturers. This organization sets energy-efficient standards that products have to meet in order to earn the Energy Star sticker. When you see a window has an energy star sticker on it, that means it has undergone rigorous testing and meets multiple energy-star criteria.

Double hung replacement windows are one of the best options to get the best R-values and U-factors. Look for ones that are Energy Star Certified.