When you need to make a decision to replace windows in your home for whatever reason, consider it as an opportunity to enhance energy efficiency in the area where the replacement needs to be done. There are many factors to justify the replacement of windows including increasing the insulation properties in your home. Installing a replacement window will require you to look at the different brands that are available and consider whether to use insulated glass and even weather stripping. You will also have to remember that a replacement window will have to fit into the existing space and will be installed on the frame of the existing window so you will have to stay within these margins or perimeters when making a selection. The replacement window can contribute to keeping conditioned air in, as well as unconditioned air out and can substantially improve the ambience in your home in the summer. In order to distinguish the different types of insulation available, first it is important to understand that there is the U factor option that allows for a transfer of energy. The other is known as the R factor that is the ability to contain energy. The best selection is to have the highest R factor and the lowest U factor in order to optimize energy efficiency.