and you aren't looking to make any alterations to the walls around them, you could look into replacing the glass and keeping the existing frames. GLASS ASSEMBLIES Single-pane windows no longer meet building codes. Your two choices are double- and triple-pane. An add-on that is often well worth the price is a low-e coating that reflects heat back into the room. You can also boost energy efficiency with windows that have either argon or carbon dioxide gas between the panes. COMPARE THE NUMBERS There's an easy way to compare the efficiency of windows since the National Fenestration Rating Council independently tests and rates most of them. The most important number on the council's label is the U-factor. The lower the U-factor, the more efficient the window is. It's best if the window has an Energy Star label; however the rating council label will tell you which Energy Star window is more efficient. You'll have to live with your new windows for several years, so be sure to do your research and consider all options. And because new window installation is a complicated process, it's best to have them installed by a qualified professional with solid references. ■ This column was co-written by Pat Keegan and Brad Thiessen of Collaborative Efficiency. For more information on creating an energy efficiency upgrade checklist, visit collaborativeefficiency.com/ energytips. This example of an NFRC label shows the U-factor rating (insulation value) and solar heat gain coefficient (amount of heat energy transmitted through the glass). co-opliving.com June 2020 | Cooperative Living | 27http://www.collaborativeefficiency.com/ http://www.co-opliving.com