The International Energy Star symbol is a simple way for consumers to identify products that are among the most energy-efficient on the market. Only manufacturers and retailers whose products meet the Energy Star criteria can call their product Energy Star. Understanding what the numbers mean:
Energy Star Zone – The Area within North America that the window has been rated for testing.
U Factor – Measures how well a product prevents heat from escaping. The rate of heat loss is indicated in terms of the U factor (U Value) of a window assembly. U factor ratings generally fall between 0.20 and 1.20. The insulating value is indicated by The R – Value which is the inverse of the U – Value.
Solar Heat Gain Coefficient – (SHGC) measures how well a product blocks heat caused by sunlight. The SHGC is the fraction of incident solar radiation admitted through a window, both directly transmitted and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a windows SHGC, the less solar heat is transmitted.
Energy Rating – (ER) an overall measure of the window’s energy performance, the higher the number the better the performance.
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