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Window 101











Air Infiltration Testing
Done to measure the amount of air flow through a window relative to the amount of wind. Normal testing is based on winds of 25 MPH. Results are shown in cubic feet per minute (Cfm). Remember, when comparing air infiltration tests, lower is better.

The relative ability of a surface to reflect or emit heat or radiation. Emissivity factors range from 0.00 to 1.00. The lower the emissivity, the less heat that is emitted through a window system. Emissivity is typically measured by U-factor or its opposite (R-factor).

A measure of a products ability to resist the transfer of thermal energy. Remember: higher is better when comparing R-values.

Solar Heat Gain Coefficient (SHGC)
Measures the proportion of solar energy penetrating a building. SHGC is expressed as a value between 0 and 1. Remember: Lower is better when comparing SHGC. U-value - A measure of rate of non-solar heat flow through a material or assembly. Lower is better when comparing U-values.

Visible Light Transmittance
Indicates the amount of visible light transmitted through the glass of a window. VT is expressed as a number between 0 and 1. Higher is better when comparing VT.