You're not sure?I would say 10
Or for the purchaser of the windows. My house was built in 1979 with single pane windows. A few have been replaced with dual pane which have the lifetime warranty. I've had one dual pane replaced under warranty. Not sure if I will replace the rest of the single pane windows. I can't tell any difference in noise or insulation value in the windows I have upgraded to dual pane, so would be purely a cosmetic decision.26.
For those with windows that go bad most have a lifetime warranty for the origional homeowner, but not for secondary owners. This isn't usually well advertised.