An Explanation of the Solar Heat Gain Coefficient

In simple terms the Solar Heat Gain Coefficient is the percentage of heat that strikes the exterior of a window that is passed to the interior of the home and is a general gauge of the window's energy efficiency. The heat gain coefficient is an important measure of a windows ability to block this heat transfer into a building and is critical to lowering cooling costs in the summer months. The less thermal energy that a window allows to enter a home, the less cooling will be required to keep the home at a comfortable temperature.

The Challenge
The challenge is that some homes are designed to incorporate passive solar heating in the winter months and with the goal to allow this solar radiation to penetrate deep into the home to warm the walls and floors. In this case you need the windows to allow the sunlight to pass through the exterior windows untouched to be able to take advantage of it. To control this heating effect in the summers these homes typically take advantage of strategically placed awnings or window blinds to control the amount of sunlight that enters the home.

Coefficient Rating
The Solar Heat Gain Coefficient rating is listed as a number between 0 and 1 and the closer to 0 your window is rated, the better it is at blocking this radiant heat from entering your home. Even though this seems like a simple metric to use when trying to gauge how well a window can block heat from invading your home, there are actually several numbers under the cover of this single coefficient rating number. The main number used for comparison by most companies refers only to the glass and glazing itself. While this is a pretty good indicator of how well a window blocks this solar heat from entering your home, it is not the only way that a window transmits this exterior heat into your home. The frame and mounting hardware are also heated by the sunlight and can transfer this heat to your home as well. The second number is usually given as a whole window Solar Heat Gain Coefficient rating and is a more representative number for the entire window.

Lowering the Gain Coefficient
The way that a company lowers the Solar Heat Gain Coefficient of a window varies by manufacturer, but usually involves the application of a particular glazing material to the window glass. This glazing typically consists of the application of a low-emissivity coating layered onto the glass and bonded. This low-emissivity coating allows the windows to reduce the amount of heat it loses in the winter months and also better controls its heat gain coefficient to increase its overall energy efficiency. By using these specialized materials to treat the glass these windows can help to make your home much more energy efficient and lower your heating and cooling bills as well. To help improve the Solar Heat Gain Coefficient of existing windows, there are several types of tinting materials that can be applied to them on-site. These tinting materials will improve the Solar Heat Gain Coefficient of these older windows and help you control your energy costs for a small investment in upgrading your windows with the tinting.