Cut Your Utility Bills

Q. I am planning to get replacement windows for my house. I currently have single pane windows. Are there any new types of super-efficient glass options in 1990? — F.G.

A. There are several super-energy-efficient types of glass recently made available for residential windows. These new windows have an insulating R-value up to R-9, as high as some house walls. They can cut your present winter heat loss and summer heat gain through windows by as much as 90 percent.

The keys to super-energy-efficient glass are special low-emissivity (low-E) coatings, multiple insulating spaces with clear insulating inert gas. In addition to saving energy, outdoor noise is greatly reduced. In cold regions, wintertime window condensation is nearly eliminated.

An insulating value of R-9 is obtained from a triple-pane window with a low-E coating on two of the panes. The 1-1/2-inch overall width provides two wide sealed spaces between the three glass panes. These spaces are filled with insulating argon gas. A narrower version yields about R-7.

R-8 glass also uses two low-E coatings. These are on two sheets of thin clear film which are stretched in between the two sealed glass panes. In effect, it’s a quad-pane window with three spaces filled with insulating gas. Using film instead of two more glass panes reduces the weight. In hot climates, special heat-rejection low-E films can be used instead.

One of the film sheets also has a special invisible coating that stops almost all the sun’s fading ultraviolet rays. The spacer around the edge, which separates and supports the film sheets, is also made of an insulating material.

Another new type of glass switches from clear to frosted at the touch of a switch. This is ideal for bathrooms or bedrooms where you want a clear view at times and privacy at other times. When it becomes frosted, light still passes through to brighten your room without lights.

This glass works by incorporating a thin liquid crystal layer (like your electronic watch display) in a pane of laminated glass. This can be assembled into an insulated double pane unit for fixed windows. When a very tiny electric voltage is applied to the window, it is perfectly clear. When you switch off the voltage, it becomes frosted.

When you talk with contractors about selecting replacement windows, make sure you specify the type of glass to be used. Since the glass area constitutes the majority of the heat loss and heat gain area, it has the greatest impact on the energy efficiency and your comfort.

You can write to me for UTILITY BILLS UPDATE No. 046 showing information and specifications on these new types of super-energy-efficient glass, the window manufacturers offering them, and styles of windows available. Please include $1.25 and a self-addressed BUSINESS-SIZE envelope.

Readers may send questions to James Dulley, c/o Bangor Daily News, 6906 Royalgreen Drive, Cincinnati, Ohio 45244. Dulley studied energy management at the doctoral level at Harvard.