Until consumers start researching windows when planning to replace their old ones, most aren’t aware of the possibilities of buying windows with “gas” between the panes. Yet gas-filled windows have more or less been the rage over the last several years. So, it’s not unusual to hear homeowners ask WHY do we want gas-filled windows?

Here’s basically what happened. Back in the 1970s and 80s, the window industry raced to see how wide a gap it could make between the panes of glass to improve the thermal efficiency of windows. Company A had ¼” thick glass, then company B developed 3/8” thick glass, so company A in turn released ½” thick glass… and the race was on.

All of these glass systems were produced with “dead” air space; just air that didn’t move. Then the labs began to notice an interesting side effect. Once the air space reached wider than roughly ½”, the air inside it began to move. It was no longer the “dead air” space that was required to improve a window’s thermal performance. In fact, the air movement inside these larger spaces actually began to draw heat out of the home rather than keeping it in! Companies found themselves asking, “What now?”

During those times, to achieve the best performance, sheet glass companies were also rushing to develop glass with very thin, practically invisible metallic coatings because the coatings worked well to reflect heat energy. This new coated glass was more expensive, but also pretty much worthless because the larger air gaps simply counteracted the thermal benefits of the coatings.

Long story short, industry professionals eventually realized that filling the air spaces with a gas heavier than air would stop the movement inside between the panes—and work better with the new glass coatings to greatly improve the thermal performance of double-pane and triple-glass windows.

There are three gas elements that are heavier than air and completely safe—and all naturally existent in the air we breathe. They are Argon, Krypton and SF6. Argon is the most common and abundant of the three. It’s also the easiest to extract, so it’s the least expensive. Krypton is more expensive than argon, but still a pretty affordable choice. SF6, however, is the least available gas of the three and thus is not a viable option.

Now window manufacturers have excellent solutions for homeowners—new Low-E-coated glass panes, combined with inert gases that are heavier than air and result in highly effective double- or triple-insulating glass systems. Windows now can achieve center-of-glass R-values in the range of 10—levels that were unheard of some years ago.