Solar Heat Gain Coefficient (SHGC) is a measurement of how well a windows stops heat from getting IN your home or how well the window blocks heat caused by sunlight. The SHGC measurement is on a scale of 0 to 1; typical ratings range from 0.25 to 0.80. The lower the SHGC, the less heat from the sun the window transmits to the inside of your home. The less heat allowed to enter your home from sunlight the lower your cooling cost.
For Energy Star qualification in the Northeast a window must have:
a minimum SHGC of "any"
While the Energy Star requirements are not calling for minimum rating the lower the SHGC the greater the cost of a window and better the energy savings. LOWER IS BETTER