When air leaks through cracks and openings in your home's windows and doors. you not only lose energy. You also lose money. At some point, simply repairing windows and doors to seal the air leaks may be too costly, time-consuming or even impossible, making it time to purchase new ones. 

Buying windows and doors can be confusing because there are many options in terms of materials, finishes, insulation and more. But one key factor to consider that can save you money over the long run is energy performance, says the Minnesota Department of Commerce.

When evaluating energy efficiency, the first thing to look for is a label from the National Fenestration Rating Council (NFRC). The NFRC provides performance ratings of windows, doors, and skylights based on several factors, including:

• U-factor. This is the ability of a window, door or skylight to conduct heat (the inverse of an R-value used to evaluate products like insulation). U-factor ratings generally fall between 0.20 and 1.20. The lower the number, the better the energy efficiency. The recommended U-factor for windows and doors is 0.30 or less.
• Solar Heat Gain Coefficient. This is a measure of a product’s ability to reduce heat gain in the summer, thus lowering cooling loads. Based on a 0 to 1 scale, the lower the number, the more effective the product. In Minnesota, a good balance of about 0.50 is recommended for windows.

Windows and doors with the ENERGY STAR® designation meet specific energy performance criteria. The NFRC label can be found on all ENERGY STAR®-qualified windows and doors. Both ENERGY STAR® and NFRC ratings include several factors that affect energy performance.

Proper installation is critical to good performance

Proper installation of windows and doors will provide the best performance. A product's improved efficiency or durability can be quickly canceled out by substandard installation or lack of attention to detail.

For more on what to look for in new windows and doors, check out the Minnesota Department of Commerce Home Energy Guide (pdf, pages 21-25) and two U.S. Department of Energy resources: “Energy Performance Ratings for Windows, Doors, and Skylights” and “Energy-Efficient Windows.” 

Minnesota Energy Tips is provided twice a month by the Minnesota Department of Commerce, Division of Energy Resources. Contact the division’s Energy Information Center at energy.info@state.mn.us or 800-657-3710 with energy questions.