Having spent more than twenty years in the heating and air conditioning business, first installing and later designing systems, I’ve witnessed firsthand the remarkable improvements in window technology, as well as its effects on HVAC system sizing.
Today’s modern Low-E windows are light years ahead of what was available just a decade ago, with advanced glazing techniques, better sealing, and double or even triple panes. All these advances have drastically lowered the solar heat load on a residence, thereby decreasing the required size of the HVAC system needed to maintain the indoor temperature.
U-value and SHGC of Energy Efficient Windows Keeps Going Down
A good way for a layman to determine the energy efficiency of a window is to look at its U-value and SHGC numbers. U-value is the thermal resistance of a window, much as R-value is the thermal resistance of insulation. This number represents the amount of heat that will be transferred directly through a window. SHGC stands for Solar Heat Gain Coefficient, and is a measure of how much solar heat is allowed to transfer through the window. The lower these two numbers, the more energy efficient the window will be.
