Heat loss and heat gain calculations are often performed to determine the size of the furnace and air conditioner required to keep the home comfortable.

A larger heating or cooling load due to a larger home, greater window area, or less insulation will require bigger heating and cooling equipment. Side by side calculations will show that low solar low-E glass helps the performance of all windows, whether exposed to the sun or not.

Even with no sunlight on the window, the summer heat gain and winter heat loss are reduced due to the improved insulation characteristics of the low-E glass.