Energy efficient metal-coated "Super Glass" on dual pane vinyl windows and patio doors cuts Heat Loss

There's a new breed of glass that outperforms just about every window on the market. A double-pane window of this new "super glass" loses up to 42 percent less heat than a standard double-pane window. It's even better than a triple-pane window because it weighs less, costs the same and can save as much or more energy.

This year, most major manufacturers have promoted the super glass in storm windows, as well as patio doors and skylights. It's sold under a zillion different brand names, but it's known generically as low-emissivity glass.

A low-emissivity window or patio door looks like an ordinary window or patio door with double pane glass in it, but there is one key difference: the inside face of the outer pane has a metallic coating that's a mere few hundred atoms thick. This microscopically-thin coating can barely be seen but it stops radiant heat loss by not emitting it to the colt outdoors. Hence the higher R-value of low-emissivity windows.

Not only will your heating bills notice this improvement but you should, too. In winter, your thermostat may be set at a warm 70ºF, yet you'll feel chilled sitting near an ordinary window. Some of that chill may be due to air leaking through its cracks, but some is also due to the radiant heat loss of your warm body to that cold glass. If your windows are skinny single-panes, the room-side surface of that glass is only 14ºF when it's 0ºF outside! If you have ordinary double-pane glass, the room-side glass temperature will be about 41ºF . But with low-emissivity glass, the room side surface will be 51ºF .

For all its benefits, super glass doesn't cost much more than standard windows.

Another type of super glass is known as Heat Mirror. It's based on the same principle of reducing radiant heat loss, but in this case the metallic coating is deposited on a clear plastic film, which is then suspended between two panes of glass. You get a window with two benefits: (1) the insulating value of a triple-pane window and (2) the low-emissivity coating for an R-value of about 4.2.

Heat Mirror was developed at the Massachusetts Institute of Technology in the 1970s, partly with federal funds, and has been in production since 1981. It is sold to various window makers, who incorporate it in their lines. Three widely-distributed carriers of Heat Mirror are Certainteed, Hurd, and Louisiana-Pacific windows.

When shopping for super glass, look for the longest warranty and the lowest U-value, . window literature generally rates energy performance in terms of U-value. The U-values of super glass vary, depending on the glass manufacturer and the type of coating. The coating can be applied to glass in two ways: by a "pyrolitic" method, while the glass is still molten, and by a "vacuum" method, once the glass is hard. The vacuum method results in a better U-value, but creates handling problems for window manufacturers, and cannot be placed in storm windows.

Click here for more on windows

You can click on blue highlighted links on the right for other products and services