Window Glass / Glass Packages
The glass package is a major part of a window's energy performance, but more panes or more coatings do not automatically make one window better than another.
Insulated Glass Units
Most modern windows use an insulated glass unit (IGU). Double-pane glass has two panes and one sealed space. Triple-pane glass has three panes and two sealed spaces.
Low-E Glass
Low-E, or low-emissivity, is a very thin coating designed to control heat movement through the glass. Different Low-E coatings and coated surfaces can be used to target winter heat loss, summer solar gain and UV exposure.
More Low-E coatings are not automatically better for every home or application. The entire glass package and window design need to be considered.
Is Triple-Pane Always Better?
No. Triple-pane glass can improve thermal comfort and may improve overall performance, but a well-designed double-pane window can outperform a poorly designed triple-pane window.
Look at the Ratings
U-Factor: Lower numbers indicate less heat transfer through the complete window.
SHGC: Solar Heat Gain Coefficient measures how much solar heat passes through the window. The ideal number depends on climate, orientation, shading and homeowner goals.
Instead of asking only whether a window is double- or triple-pane, ask for the U-Factor and SHGC of the complete window.