U-factor measures how well a product prevents heat from escaping a home or building. U-factor ratings generally fall between 0.15 and 1.20. The lower the U-factor, the better a product is at keeping heat inside the building. U-factor is particularly important during the winter heating season in colder climates. This label displays U-factor in U.S. units. Labels on products sold in markets outside the U.S. may display U-factor in metric units.What are the other options to consider when shopping for windowsu-value-11?

 
In addition to the NFRC Label, ratings comparisons, and ENERGY STAR, buyers may consider a number of other factors when choosing windows. These include: air infiltrationwater infiltrationstructural performanceacoustical performance, security performanceproduct cost, and warranty. All of this information is provided by A1.