Solar Heat Gain Coefficient
Every day the sun rains down massive amounts of energy on your home. In colder climates and winter months, this energy can be beneficial, warming our homes and reducing our energy costs. Properly designed solar energy panels can convert this energy into usable energy for your home. However, for homes in warmer climates this solar energy creates increased energy costs.
The majority of solar heat gain comes through windows, glazed doors, and skylights. The best way to manage the amount of solar gain that enters your home is to block it before it enters. One way to accomplish this is to install replacement windows with a low Solar Heat Gain Coefficient (or SHGC) rating.
The National Fenestration Rating Council (NFRC) has created a standard method for rating the amount of solar heat gain that is admitted through a window. This standard allows for a uniform system for indicating the ability of a window or other glazed product to admit solar heat gain. SHGC is expressed as a number between 0 and 1. The lower the SHGC rating, the better the ability of the window to block the heat from the sun.
SHGC ratings express the performance rating for the entire window, not just the glass. Therefore the type of window, as well as the glass can affect the SHGC rating. The ability of glass to block solar heat gain is very important in the overall SHGC rating. There have been remarkable advances in the window manufacturing industry in the use of spectrally selective glass. This type of glass typically has a spectrally selective low-e coating that actually blocks or re-radiate the suns energy, reducing solar heat gain through windows.
U-Factor & R-Value
The difference between U-Factor and R-value is that U-Factor measures the rate of heat transfer (or loss) while R-value measure the resistance to heat loss (conductivity). A product with a higher conductivity will transfer heat quickly. U-Factor takes into consideration more than just conductivity. It also is affected by airflow around the window and the ability of its surface to absorb energy.
U-Factor measures how well a product prevents heat from escaping from your home. U-Factor ratings generally fall between 0.20 and 1.20. The lower the U-Factor, the better the product is at keeping heat in. U-Factor is particularly important during the winter months.