These Third Party Organizations Test and Define the Efficiency of Each Window.

NFRC- National Fenestration Rating Council tests overall Thermal Performance. They test for the following factors:

• U-Factor- measures the rate of heat loss or how well a window prevents heat from escaping.
  • Ratings generally fall between 0.20 and 1.20, the lower the U-Factor the greater the resistance to heat loss. A lower U-Factor will make you window more energy efficient.
• SHGC- The Solar Heat Gain Coefficient- measures how well a product blocks heat caused by sunlight.
  • The SHGC rating is expressed as a number between 0 and 1. The lower the SHGC the less solar heat is transmitted through the window, and the cooler you house will be.
• VT (Visible Transmittance of Light)- measures how much light comes through a window
  • VT is expressed as a number between 0 and 1. The higher the VT the more visible light is transmitted through the window.

Energy Star

• Energy Star itself DOES NOT measure anything
• It uses NFRC overall window thermal test results to assign geographical "Zones." Depending on where you live and your climate Energy Star recommends certain U-Factor and SHGC levels
  • Energy Star qualifying ratings for the Greater DC Area are:
    • .32 U-Factor or less
    • .40 SHGC or less
• It does not take into account AAMA Air, Water, and Structural test results

AAMA (American Architectural Manufacturer's Association)

• An AAMA Window Certification requires three (3) tests: Air Leakage, Water Leakage, and Structural Strength. AAMA Certified windows have an affixed label located inside the head of the frame. AAMA Gold Label Certified Windows, are the best, they have to pass both AAMA and NFRC standards.
  • Air Leakage- Windows either pass or fail this test, any window with an infiltration number above 0.30 cfm at 25 mph fails. The lower the number the less air infiltration into your home.
  • Water Leakage- windows are subjected to 8 inches of rain per hour and increasing wind loads until water leaks through the window.
    • The minimum standard is 33 mph
  •   Structural Strength- increasing wind is blown against the window until it breaks.
    • The minimum standard is that a window must withstand 94 mph

WDMA (Window & Door Manufacturers Association)

• Promotes, protects and advances the use of high-performance, high-quality, windows, door and skylights through advocacy, educations, standards and certifications.