"E", "R" & "U"

Natural sunlight illuminates a space as no light fixture can. However, it also allows in damaging UV (ultraviolet) rays that can cause colors to fade and increase the passive heat in a room. Window and door manufacturers address these two issues by glazing the glass and increasing the insulation and R-Values of the glass, frame, sash, and door parts. Low E stands for "low emissivity". Low E glass is standard glass that has been coated with microscopic metal or metallic oxide to reflect or absorb the sun's warmth. This means reduced passive heat in hot weather and reduced heat loss in cold weather. It also helps protect against damage from UV rays. According to Herrick Kimball, author of "The Kitchen Consultant", "Low E windows are about 30% more energy efficient than standard insulated glass".

The R-Value indicates the resistance a material has to heat flow. The higher the number, the greater its insulating capabilities. Standard glass has no insulating or ultra violet protection--thus the need for storm windows to reduce heat flow. Today, double pane windows are almost standard issue. When double (or triple) panes of insulating glass are used, manufacturers can fill the air space between the glass with an inert gas (usually Argon Gas) to further minimize heat transfer. Also, double (and triple pane) windows do not need the additional storm windows.

The "U-Factor" is the measure of total heat flow through a window or door barrier from room air to outside air. The lower the number the greater the insulating capabilities.