A key component to every window is the glass. In most windows, the glass is the least efficient element making it one of the most important in the overall performance of the window. The glass (and the window as a whole) is evaluated by its U-value (insulating performance) and Solar Heat Gain Coefficient (SHGC – a fraction of the amount of solar radiation allowed by the glass). The lower the U-value, the better the insulator the glass is (ratings from 1 to 0, where 0 is the best). The lower the SHGC, the less solar heats the glass allows through and the greater its shading ability.
Over the last couple of years, the glass technology has improved. For many years, double pane insulated glass with basic low emissivity coatings (also known as Low e or LoE) was one of the best products available. This soft coat silver metallic coating inside of the sealed glass unit, typically has 1 (Low E) or 2 (Low E2 – squared or Solarban 60, SB60) microscopic thin layers of silver that allow visible light through, but reflect a certain amount of harmful uv rays and unwanted radiation. This Low E “smart” glass actually reflects the raditation back to the source and based on the angle of the sun, it will allow more heating rays during the cold winter months and block these same rays in the hot summer months. During the winter, it will also reflect heat back into the house instead of letting it escape outside.
The latest advancement in glass coating technology is Low E3 (cubed or Solarban 70, SB70). This new glass coating has a third layer of microscopic silver. You might ask, why not add a four layer of silver? Well, it basically turns the glass into a mirror and doesn’t allow enough light to pass through. The metallic layers are specifically applied in a manner that allows visible light to still pass through, but it blocks even more harmful uv rays (up to 95%). This means that there is virtually no opportunity for carpet, curtains and furniture to fade from uv rays. More, the glass is a superior insulator and that means lower energy bills and warmer rooms.
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