Do your new replacement windows have the best glass?
January 31, 2012
Many times when I present a window's features to a potential customer, they ask me for the "best glass" that particular window company offers. All window manufacturers in the U.S. buy their glass -- other than imported glass -- from the same four or five major U.S. glass suppliers: Cardinal, PPG, Pilkington, Guardian and AFG. Each manufacturer differentiates its glass offerings with its own brand names for low-e, tinted, laminate and heat-resistant glass, but their products all perform similarly.
When you look for the best glass for your windows, the most important consideration is the climate zone in which you live. Each of the four U.S. zones requires its own insulating and solar heat gain values for window glass to meet or exceed Energy Star requirements. There are several types of low-e glass that meet these requirements.
How is low-e glass made?
Low-emissivity (low-e) coated glass is made by either one of two methods -- hard coat or soft coat. Hard coat -- pyrolytic coating -- is applied when the glass is still semi-molten, and it becomes part of the glass. Soft coat, on the other hand, is sprayed -- "sputtered" -- onto the cooled glass while in a vacuum. The number of coatings each type of glass receives corresponds to Energy Star's low-e requirements for the glass's insulating and solar heat gain values.
Each manufacturer gives brand names to their various types of glass; for example, Cardinal offers 366-Low-e3 and 270-, 272- and 240-Low-e2. PPG has several levels of solar-control low-e glass with names such as SolarBan 70XL, Solarban 72, and Solarban 60. AFG's offerings include Comfort E-PS and Comfort Ti.
Some of the window manufacturers you might be considering have borrowed and use these brand names with their own brand names appended to distinguish the different types of glass offered in their windows. The only thing you really need to know, however, is whether the low-e glass in the windows you're planning to buy meets the requirements for your climate zone.
So how do you know if you're getting the best glass? Know the Energy Star requirements for your geographical location. If the properties of the glass used by the manufacturer meet those requirements, you've got it.