How do i know if my windows are energy-efficient?

The most accurate and reliable way to determine if your windows are truly energy-efficient is to inspect the glass or frame for an official certification label from the National Fenestration Rating Council (NFRC). This standardized label provides objective performance metrics, including the U-factor (which measures how well the window prevents heat from escaping) and the Solar Heat Gain Coefficient (which measures how effectively it blocks heat from the sun). If the labels have been removed, you can look for physical indicators of modern efficiency. Energy-efficient windows almost always feature double or triple panes of glass rather than a single pane. Furthermore, if you look closely at the edges, you will see a warm-edge spacer separating the panes, which often house an invisible insulating gas fill like argon or krypton alongside a microscopic low-emissivity (Low-E) metallic coating.