One bigger hit and its gone and you will not even know it till it fogs. Even argon glass of same pressure as air can eventually leak out and be replaced by air, reducing its efficiency significantly.
Are these big national-brand window companies that provide "lifetime warranty" just cashing in today and hoping for the best (bankruptcy) exit strategy later when all their installs from this generation fail in a couple decades?
Not installers, but companies like Pella, Window World, et al.
They may define "lifetime" as "25 years" or limit the warranty to the original purchaser, knowing that most people don't live in one house that long, or count on the later owners not realizing that there is a warranty, or knowing when or from whom the windows were purchased.
Yeah, there's a disturbing trend of products advertising a "lifetime warranty", only the fine print says that the "lifetime" in question is the "lifetime of the product", which is whatever the manufacturer says it is (usually no better than the competition).
These warranties typically only cover issues due to manufacturing. If your window fails decades later they'll just say it wasn't due for manufacturing.
