How To Save Energy
Reduce energy loss in your home by increasing the quality of your windows and doors. You can tell almost everything you need to know about a window's performance by looking at its "NFRC label". Adopted by the National Fenestration Rating Council in 1998, this label is affixed to windows voluntarily by manufacturers concerned about energy efficiency. If a window does not have this label, chances are you're not dealing with a reputable manufacturer.
U-Factor: The inverse of "R-Value" (which measures insulating value), the U-Factor measures how easily heat flows through the product. The lower the number, the better it keeps heat where you want it. In cold climates, look for a U-Factor of 0.35 or lower.
Solar Heat Gain Coefficient (SHGC): The SHGC tells you how much heat radiation from sunlight a window lets in. If heating your home is your main concern, a higher SHGC can help offset some of the heating costs. In warmer climates, where air-conditioning costs are a bigger factor, look for a lower number.
Visible Transmittance (VT): The Visible Transmittance number indicates the amount of light that passes through the glass (refers to brightness, as opposed to heat). A higher number means a brighter room.
Air Leakage (AL): The Air Leakage rating refers to the amount of air that can infiltrate cracks in the window assembly. The lower the number, the less infiltration. Look for windows with an AL rating of 0.30 or less.
Res/Non-Res: The NFRC label contains data for "Residential" and "Non-Residential" (industrial) windows. When shopping for windows for your home, be sure to compare the "Res" numbers.