subject: What Is The Best Window For Your Home? [print this page] If you've ever seen an early 1900s window, you would discover that it has many ripples in the single pane of glass set into a wooden frame - which is really different from the most energy-efficient, double-paned, vinyl framed windows we have nowadays.
Although window glass has steadily improved through the decades, insulated windows - two or more pieces of glass with dead air between them - made their first appearance in the 1970s. The windows restricted the change in temperature and cut down on condensation by providing dead air space.
Ten years later, low-e glass was introduced. To prevent heat and ultra-violet (UV) rays from coming through , low-e coatings, which are extremely thin layers of metallic oxide, are bonded to the surface of the window's glass. Due to this, windows have become more effective at keeping heat out during summer and in during winter.
We cannot see infrared or UV rays but they makeup most of the sun's energy. Causing sunburns are not the only thing UV rays can do, they can also fade furnishings and finishes inside the home. Infrared rays produce heat, whether on the asphalt outside, or from the furniture and flooring indoors. If you let it in, infrared heat can affect your home even after the sun sets because this heat is retained and released as the air around them cools.
Low-e coated glass, however, reflects selected portions of the light spectrum back out through the windows, meaning the inside of the home stays cooler, not only during the sunny part of the day, but later as well.
You can choose from either hard coat or soft coat low-e glass, which are both being offered today. To produce the hard coat, tin is directly applied to the molten glass. In soft coat, a thin layer of silver is applied to the glass in a vacuum. Easily damaged soft coat low-e glass is always sandwiched with another piece of glass. Argon gas is often used between panes to prevent oxidation and also acts as an additional insulator.
A third type of low-e glass is heat mirror, which includes a thin polyester sheet suspended between the two panes of a dual pane window. If you live in extreme climates, the coating reflects radiant heat and the sheet decreases heat loss, which makes this the best option for you. As much as 99.5 percent of UV light is blocked by the film and it increases insulation by as much as 100 percent.
Be certain that the kind of windows you want are a match for the climate in which you live in before buying them. To be sure, look for the Energy Star or National Fenestration Rating Council (NFRC) label. Included in the NFRC label should be the U-value and the solar heat gain coefficient (SHGC) for the window. Although there is no SHGC requirement because solar heat gain is not an issue to comply with Energy Star standards, in the colder areas the U-factor should be .35 or less, while in the hottest areas windows should have an SHCG rating of .4 or lower and a U-factor of .75 or lower.
