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Windows and doors need to be more than just beautiful. They need to function in the harshest of climates, so that your house stays warm in the freezing cold and your house stays cool in the scalding sun. These ratings help you decide which windows and doors perform best under pressure, so that you can stay comfortable no matter what Mother Nature brings.
Energy Star Ratings - Glossary of Terms:
The Energy Rating, also referred to as an ER number, is one measure of energy efficiency for a window or door. The number is calculated by combining losses due to air leakage and heat transfer (u value) with gains from solar heat (SHGC). The higher the number the better.
The U value indicates the rate of heat transfer. The lower the u value, the slower it transfers heat from a warm area to a cold area, and the better it insulates. U value is the inverse of the R value which is commonly used to measure the insulating properties of a material.
The Solar Heat Gain Coefficient (SHGC) is a measure of the ratio of solar radiation that enters a building through a window as heat gain. SHGC is measured on a scale from 0 to 1 with values typically ranging from 0.25 – 0.8. A high coefficient means more solar heat is captured.
Visible Transmittance (VT) is a measure of the amount of visible light that enters a building through a window. VT is measured on a scale from 0 to 1 with values typically ranging from 0.2 – 0.8. The higher the number the more light you see.
Condensation Resistance measures how well a product resists the formation of condensation on its interior surface. The value is calculated on a scale from 0 to 100. The higher the number the better the product is at resisting condensation.
