Glossary of Window Terms

Low E Glass
Glass with a transparent metallic oxide coating which allows short-wave energy to pass through but reflects long-wave infrared energy, improving the U-value.
U-value
The U-value or U-factor is commonly described as the amount of heat transferred through a material. The lower the U-factor, the slower the rate of heat flow and the better the insulating value.
Visible Transmittance
Visible Transmittance (VT) measures how much light comes through a product. The visible transmittance is an optical property that indicates the amount of visible light transmitted. VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted.
ENERGY STAR
ENERGY STAR® is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy helping us all save money and protect the environment through energy efficient products and practices. Windows and doors that meet ENERGY STAR guidelines have been tested for optimum energy efficiency.
Argon Gas
This odorless, colorless, non-toxic gas is six times denser than air. When used to replace air between glass panes in insulating glass units, it helps reduce temperature transfer.
Solar Heat Gain Coefficient (SHGC)
The SHGC refers to the amount of heat from the sun that windows and doors allow into the home.
The lower the number, the greater the ability to reduce the amount of heat absorbed into the home.
United Inches (UI or ui)
This is a term referring to the size of a window and this is the determining factor in establishing the price of any given type of window.  UI is determined by adding the width to the height.  So a window that is 36″ x 60″ is 96ui.  In general, window pricing is bracketed by window type and it’s size.  For example, all double hung windows under 99ui are the same price. From 100-110 they are one price. From 111-120 they are one price. From 121-130 they are one price and so it goes in 10 inch increments to it’s max size allowance. This is the main reason we can receive “generalized” (not exact) measurements from homeowners and give accurate replacement window quotes without having to come to your home to measure them ourselves. We can even tell the “bracket size” of a window from the pictures found on Google maps by comparing the window to the “standard” 36×80 front door or by counting the grids in the windows.  That’s why many times, we’ll ask you to measure only the largest windows in the house. Once you get to a window size under 99ui, you don’t need to do any more measuring.