Argon filled units also cannot use breather tubes for high altitude applications.
Argon filled windows at high altitude.
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.
It is also likely that water vapor will gradually enter the ig unit resulting in fogging if enough moisture gets in.
While an air filled gap between two panes helps improve window efficiency argon or krypton gas infills are even better.
One competing window rep claims that all windows regardless of elevation will lose their gas fill over time because of the small size of the argon or krypton atoms.
Argon permeation is greater than air for most ig sealants which can result in negative pressure in the ig air space.
These units will not qualify for the tax credit and will not meet energy star northern region.
I have a couple of concerns about the longevity of the gas fill.
Milgard is now making windows in salt lake city and offering argon gas as an option to those of us at 6000.
When windows filled with argon are transported and installed in buildings above 5 000 ft however lower atmospheric pressure causes the argon gas to expand which in turn can lead to adverse effects.
Secondarily we can sell the windows with capillary tubes or air filled.