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Window
performance (R=5)
Insulation filled vinyl frames
Low-E Argon filled glass
U-factor = .22 (lower is better)
Solar Heat Gain Coefficient = .22 (lower is better)
Visible Transmittance = .5 (higher is better)
Energy Star and NFRC (National Fenestration Rating Council)
Certifications
Door performance
Insulation
filled fiberglass
Low-E Argon filled glass
U-factor = .3 (lower is better)
Solar Heat Gain Coefficient = .3 (lower is better)
Energy Star and NFRC (National Fenestration Rating Council)
Certified
What do these numbers really mean?
U-Factor
U-Factor is a description of the rate of heat loss through a window assembly, or put more simply, it describes how well a window insulates. The lower the U-factor, the greater a window's resistance to heat flow and the better its insulating properties.
Interestingly, while the U-factor is used to express the insulation value of windows, R-value is used for insulation in most otherparts of the building envelope (walls, floors, roofs). R value and U-factor are directly related. To compare R-value and U-factor, divide 1 by the U-factor number, E.g.: a 0.25 U-factor equals a 1/0.25 = 4 R-value.
At U-factor .22, this project’s double-pane windows are high performance. The highest performing windows, typically triple pane windows, can achieve U-factors as low as 0.15.
Solar Heat Gain Coefficient (SHGC)
The SHGC describes how much solar radiation (heat) passes through a window. It is a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits.
This project’s SHGC is .22, which is a typical value for high performance double hung windows.
Visible Transmittance
The visible transmittance (VT) indicates the amount of visible light transmitted through a window. It is calculated by including not only the glass, but the frame as well. The higher the VT, the more light is transmitted.
While VT theoretically varies between 0 and 1, most values among double- and triple-pane windows are between 0.30 and 0.70. This projects windows are .5.
Many thanks to the Efficient Windows Collaborative for these definitions. Please see www.efficientwindows.org for more detailed information about windows performance.