Installing low solar heat gain low-E glass instead of standard double pane will typically cut the solar heat gain of the window by about one-half. That same low E-glass will also reduce the window U-factor by 20% or more, because the low-E coating insulates much better than uncoated glass.

The frame material has a relatively small impact on SHGC where smaller frames mean more glass area and larger frames block more solar heat. However, the frame material plays a major role in reducing the overall window U-factor, even with the same insulated glass unit installed in each of the frame types.

A window with a thermally improved aluminum frame may have a U-factor 15% lower than one with a solid aluminum frame. A wood or vinyl frame window may have an overall U-factor of about 40% less than a window with a standard aluminum frame.

Be sure to check the NFRC label to make your own comparisons, since the variations may be even more for specific window brands.