Argon- and Air-filled IGU

Should I use an argon- or an air-filled IG unit?

Insulating Glass Units (IG Units) can be made with air or other gases between the two lites of glass. While air itself is a good insulator, filling the gap between the glass panes with a lower-conductivity gas such as argon can improve performance by reducing conductive and convective heat transfers. This phenomenon results from the fact that the density of the gas is greater than the density of the air. Air-filled IG units are commonly used in commercial applications. However, an argon-filled IG unit sometimes might be required in order to meet specific requirements and energy codes.

Filling with an inert gas makes sense along with the installation of a low-emissivity coating on glass, otherwise the performance will improve slightly.