What is “U Value”?

Posted at 9:19 AM, January 20, 2019 by / Category:

The heat transfer coefficient (k- or U- value) is the amount of heat in watts per unit of time, which is transferred through 1 sq.m of glass surface per degree Kelvin difference between internal and external temperature. A measure of the rate of non-solar heat loss or gain through a material or assembly. The lower a window’s U-value, the less non-solar heat it transmits.