The amount of heat gained through glass taking into consideration the effects U-value and shading coefficient. The English System relative heat gain is calculated as: RHG = (Summer U-value x 14°F) + (Shading Coefficient x 200). The Metric System is calculated as: RHG = (Summer U-value x 7.8°C) + (Shading Coefficient x 630). The lower the RHG the more the glass product restricts heat gain.