U-FACTOR Solar Heat Gain Coefficient Visible Transmittance Air Leakage 4 Ways to Evaluate WINDOWS
U-FACTOR The rate of heat loss is indicated in terms of the U-Factor of a window assembly. The insulating value is indicated by the R-Value which is the inverse of the U-Value. The lower the U-Value the greater a windows resistance to heat flow and the better the insulating value. U-FACTOR
The SHGC is the fraction of incident solar radiation admitted through a window. SHGC is expressed as a number between 0 and 1. The lower a windows solar heat gain coefficient, the less solar heat it transmits. Solar Heat Gain COEFFICIENT
The visible transmittance is an optical property that indicates the amount of visible light transmitted. Theoretical values vary between 0 and 1, but most values are between 0.3 and 0.8 Visible Transmittance
Heat loss and gain occur by infiltration through cracks in the window assembly. Air leakage is expressed in cubic feet of air passing through a square foot of window area..3 is recommended for Oregon Air Leakage
Glass is coated with silver or tin oxide which allows visible light to pass through but reflects infrared heat radiation back into the room. Reduces heat loss in cool climates Allows visible light to pass through but reflects infrared heat radiation away from the room, admits up to 40% less radiant heat from the sun. Reduces heat gain in warm climates Low-E Windows
High number for cold climate. Low number for warm climates The lower the number the better the insulating value The best windows have air leakage rating between 0.1 and 0.6 cfm/ft. Varies from 0 to 1.0 The higher the # the more light is transmitted.