What do you need to know? Q. What three values are important when considering a specification for glazing material? A. Light transmission, shading coefficient/solar heat gain coefficient, and U-value. Q. What is U-Value? A. The measurement of heat gain or loss through glazing due to environmental differences between outdoor and indoor air. Q. What is shading coefficient (SC)? A. It is the ratio of solar heat gain through a glass compared to 1/8" clear glass. Q. What is solar heat gain coefficient (SHGC)? A. It is similar to the shading coefficient but also accounts for absorbed, convected, and inwardly radiated solar energy. The SHGC can be calculated by multiplying the SC x .86 (SHGC=SC*0.86). Q. What is light transmission? A. The percentage of light that passes through a glazing material. Q. What is Low-E glass? A. Thin metallic layers are applied to the glass substrate during the float process, (pyrolytic or hard coat), or after the float process, (sputter or soft coat), giving the glass excellent solar control properties. Q. What does the E stand for? A. Emittance is the property that measures the ability of the glass to absorb and re-radiate energy. Low-Emissivity, (Low-E) glass indicates a better insulating product. Q. How does Low-E work? A. Heat energy is comprised of long and short wave radiation. Low emissivity coatings help reflect the long wave heat energy back towards its source. The primary purpose of Low-E glass is to improve the insulating value. (U-Value). Q. Which Low-E is better. Pyrolytic or sputter? A. For ease of handling and fabrication a pyrolytic is better. For performance values the sputter coat is better. Q. Which surface of an insulated unit should the Low-E be on? A. Depending on your particular performance requirements, the Low-E can be on the #2 surface, (to control solar heat gain), or the #3 surface, (to control heat loss). Q. Can Low-E be tempered or heat strengthened? A. All fabricators have been tempering the pyrolytics (hard coats) for many years. Because of its hard surface it requires no special handling or tempering furnace. Very few of the fabricators have mastered the art of tempering the soft coats. One supplier, PPG Industries, requires the fabricator to pass an audit of their operation before they will certify them to handle their high performance solar control glass, Solarban 60. We are proud to say that we were the second fabricator in the nation to become a Certified Fabricator. Q. Can tinted glass be used with a Low-E glass? A. Yes. Tinted glass is very effective when used in conjunction with a Low-E glass. This combination will reduce excess heat gain and lower cooling costs. Q. How do you determine the surface number? A. The outboard surface of an installed lite of glass is the #1 surface. Every surface after that is numbered in sequence. Example: Q. What creates thermal stress? A. When exposed to sunlight, glass will absorb solar energy causing the glass temperature to rise. If glazing or shading conditions allow the center and edges of the glass to be significantly different temperatures it will create a thermal stress.