What Is Solar Gain?

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  • Written By: Pablo Garcia
  • Edited By: O. Wallace
  • Last Modified Date: 19 October 2019
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Solar gain refers to the increase in temperature that occurs when the energy from the sun passes through windows or doors. It is essentially a type of greenhouse effect. It raises the temperature in an area in the same way that a glass greenhouse protects plants and flowers from the cold. Depending on the climate or the seasons, it can be beneficial or detrimental. New technologies and building materials can manage solar heat gain to maximize the comfort and minimize the energy costs of homes and offices.

In colder climates solar gain can be beneficial, helping to reduce heating costs. It can also generate hot water and heat. In warmer climates the excessive solar energy can create a thermal load that has to be reduced by the use of air conditioning. The amount of solar energy escaping or entering a building can be managed by using appropriate materials for “fenestration” or windows, doors, and skylights.

Different types of fenestration glazes can keep the sun’s heat out or trap it inside. In “passive” solar building design, architects use various types of tinted or coated glass to allow solar energy to pass more easily into a structure and to trap and retain it. Fenestration can also be sealed or coated to block or reradiate solar heat away from a structure.


An indirect solar gain system places a “thermal mass” such as stone or liquid between the sun and the space to be heated. A structure is designed so that the hot air becomes trapped with the walls. It is then forced to rise through vents in the ceiling. A continuing supply of solar energy pushes the heat through the structure. With proper coatings and insulation, the warm air continues to circulate.

Solar energy that enters through fenestration is measured by the solar heat gain coefficient (SHGC). The lower the SHGC of a door or window, the more sunlight is being blocked or reradiated away from the structure. The National Fenestration Rating Counsel rates and certifies the SHGC of fenestration. It also rates and certifies the “U-Factor” of fenestration materials, which gauges how well a material will prevent heat from escaping. The lower the U-Factor, the better the material stops heat loss.

NFRC also rate other fenestration qualities besides solar gain, such as condensation resistance and air leakage. Some states now require NFRC certifications for all new constructions. NFRC believes that most builders know about certification requirements, but that many suppliers may not. It provides free information to consumers regarding certifications.


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