I have the Pella Designer casement windows. As I've mentioned in the past, I have huge condensation problems with them even with very low RH. I'm below the recommended 30% for 0-10F...and they still go crazy. I have a few windows that aren't of this type, and they do just fine. At some point, these windows just need to go.
The one thing I wanted to try is to see if the 3pane has less issues than what is in there now (probably 2-pane). I've heard from a few people that they've had some 3 and 2 pane Designers; their 2[anes had issues, but the 3panes did not. Does anyone know if the 2pane and 3pane inner glass panes are interchangeable?