We can specify argon filled units if the job site altitude and the nature of the window is such that the structural integrity and warranty can be maintained.
Argon filled windows at high altitude.
Secondarily we can sell the windows with capillary tubes or air filled.
It is also likely that water vapor will gradually enter the ig unit resulting in fogging if enough moisture gets in.
Argon filled units also cannot use breather tubes for high altitude applications.
Milgard is now making windows in salt lake city and offering argon gas as an option to those of us at 6000.
I have a couple of concerns about the longevity of the gas fill.
When windows are filled with a special low conductivity gas such as argon or krypton it is clear that those gases will be lost over time if capillary tubes are left open.
Argon permeation is greater than air for most ig sealants which can result in negative pressure in the ig air space.
There are also concerns about maintaining the gas fill levels over time.
While an air filled gap between two panes helps improve window efficiency argon or krypton gas infills are even better.
These units will not qualify for the tax credit and will not meet energy star northern region.