The most cost-effective time to install high-performance windows is when a building is new, or when window replacement is necessary. Quality windows create a more comfortable space while reducing heat loss and condensation. Windows labeled ENERGY STAR^? perform significantly better; typically they have a low E coating, argon gas filling, and a warm edge spacer between panes of glass.

ENERGY STAR labeled windows in a northern climate display a National Fenestration Rating Council (NFRC) label with a unit U value of no more than .35. Lower numbers mean more savings. All major window manufacturers have double pane windows with NFRC label U value of .32. Check the window label to verify that the unit is ENERGY STAR labeled for a northern climate. ENERGY STAR criteria for southern climates identify windows that reduce solar heat gain.

For office buildings with large cooling loads, using windows with low Solar Heat Gain Coefficients (SHGC) can further reduce cooling loads, particularly with windows of a western or southwestern orientation. Look for windows with an NFRC certified SHGC of .35 or less.

Daylighting decreases your need for electric light, creates a pleasant environment, and can have a positive impact on worker morale and student performance. Windows and skylights are used in conjunction with energy-saving controls that automatically dim electric lights when daylight is sufficient. Daylighting benefits are optimized by controlling glare, and by using dimming light fixtures, photocells, and occupancy sensors together as an integrated system.

Learn more about daylighting.