Vacuum-Sealed Windows Promise Better Insulation

We reported on vacuum-sealed insulating glass in 2010, and it looks as though windows that have this glass finally might arrive on the market in 2014, according to one manufacturer.

Further, we expect these windows to provide R-12 insulating performance from glass that’s expected to be just three-eighths of an inch thick. (A product’s R-value indicates how well that it prevents the transfer of heat and is based on tests by each manufacturer. It’s the inverse of the U-factor, which is the traditional measurement for window efficiency—the R-value is 1 divided by the U-factor.) For comparison, clear double-pane glass, which is typically one-half of an inch to three-fourths of an inch thick, depending on the air space that’s between the panes, is rated at R-2; triple-pane glass, which typically is about 1-inch thick, is rated at R-4.3. The thickness of multipaned windows varies from manufacturer to manufacturer and even between a manufacturer’s own products, depending on the air space that’s between the panes.

Vacuum-sealed insulating glass has two panes that are close together with a vacuum in between, so it appears to be a single pane. This makes high-performance windows an option in situations where the look of single-pane glass is important—an old house that’s striving for historical accuracy—but where you still want insulating properties that single-pane glass doesn’t have. At press time, Guardian Industries reported that the development of its vacuum-sealed insulating glass was complete, but it had yet to align with a window manufacturer to include it in a finished product. However, manufacturer Ply Gem tells us that it might introduce windows that have vacuum-sealed insulating glass by 2014. Ply Gem wouldn’t discuss pricing, nor would Guardian, although the latter said in 2010 that it was aiming for prices to the manufacturer that are similar to that of triple-pane glass. Triple-pane-glass replacement windows start in the range of $450 for a 3-foot-by-5-foot double-hung window.