ENERGY EFFICIENCY The Learning Center When you compare energy efficient windows, the first thing to consider is the window's U-value. U-values (Btu/hr-ft2-oF) are a measure of thermal conductivity. When some window manufacturers tell you the R-values of their windows, they usually give the center-of-glass value, which is considerably higher than the whole window rating. Whole window ratings, introduced in 1989 by the National Fenestration Ratings Council (NFRC), reflect the insulating value of the glass, the sash (where applicable), and the frame. 9. What are NFRC window performance ratings? < back to list of questions about energy efficiency

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1-877-SWING CLEAN info@energyswingwindows.com 3245 Miracle Drive Murrysville, PA 15668 724-387-2991 PA Contractor ID PA001856