The ER system accounts for the following factors:

Window effectiveness in energy efficiency is measured by:

• U-Factor: A factor/rating that outlines the window insulation effectiveness/rate of heat loss from the window. A window with a lower U-Factor has higher energy efficiency. The U-Factor is not limited to the glass part of the window but also includes other components, including the frame and spacers.      Annual heating and cooling energy demand decreases by 7.9–16.7% when changing the U-value of the windows in a poorly insulated house.  ​​

• Solar Heat Gain Coefficient (SHGC): A factor that reflects how much solar heat the window absorbs. A lower SHGC coefficient means less solar heat gain which can prove to be beneficial but also a drawback depending on your climate and your personal preferences.     Windows to the East and West have the highest SHGC due to maximum exposure to the Sun and therefore, if your windows face this direction, including a shading option can be beneficial to minimize heat gain during summer. If your air conditioning load is particularly high, it is important to consider whether SHGC can be driving up your heating in the summer and use low SHGC windows. In Canadian winters, this feature can however decrease your heating costs - so it is a delicate balance. The SHGC affects your cooling load more than your heating load.