All things being equal and assuming no leakage, how long can i reasonably expect the argon in a window to last before it breaks down/disapates in a good, high-end window? how about Kypton?
I ask because a) the RBA sales dude was touting that they warrant their argon + gas X mix for 10 or 20 years (i forget) and b) seems silly to spend the extra money if it breaks down in just a few years.
I'm in the "starting to finall grok all the terms phase" of buying replacement windows and improved long term energy effeciency is one of my concerns/goals for the replacements. Currently i have an entire wall 1982 era anderson north facing fixed pane windows in the Lancaster, PA area that seem to just leak heat in the winter.