Milgard is now making windows in salt lake city and offering argon gas as an option to those of us at 6000.
Argon filled windows at high altitude.
These inert gases are denser than regular air so they slow heat transfer to a crawl keeping more of the heated air inside your high altitude home.
I have a couple of concerns about the longevity of the gas fill.
Argon filled units also cannot use breather tubes for high altitude applications.
These units will not qualify for the tax credit and will not meet energy star northern region.
There are also concerns about maintaining the gas fill levels over time.
Argon permeation is greater than air for most ig sealants which can result in negative pressure in the ig air space.
It is also likely that water vapor will gradually enter the ig unit resulting in fogging if enough moisture gets in.
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.
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.
Secondarily we can sell the windows with capillary tubes or air filled.