You should assume that all doors with double-pane glass areas large enough to fit a 3-inch sphere through them are made with tempered glass (or in some cases, laminated safety glass).

So, what you have here is a double-pane window, which means there's a piece of plate glass on the outside and the inside but the inside of the glass is filled with argon gas.

Triple-paned windows, which cost about 20 percent more than double-paned, increase the energy efficiency of the glass surface up to 50 percent. Each double-paned window, installed, costs $350 to $500.

A seal failure, though, will “oxidize” the low-E coating and argon gas, making the glass appear streaky or foggy. Technically, yes, gas could be added to the window.

Plus, double pane windows are typically insulated further with argon gas injected between each pane. The chemical is used for thermal insulation, allowing the temperature of the glass to be more ...

Now you can get windows that are double- or triple-paned, windows with argon or krypton gas, low-E coatings in between the panes — and different combinations of each, like low-E double-paned ...