I purchased Pella windows for my home that I was the General Contractor for. On several of them the aluminum cladding on the outside is coming loose, and on the Pella sliding glass door as well.
On the two casement windows in my master bedroom the air leaks right through them. You can feel the cold air hitting you in the face. Last winter I put plasic up in one window and when it was windy out the plastic would bellow out as tight as a balloon. In my front bedroom the 3 windows in there have mold growing along the bottom from the air leakage and condensation buildup.
When I called Pella to complain about the casement windows which are still under warranty, the customer service rep. wanted to blame me for the situation. When I asked to speak to a supervisor magically none were available.
I would strongly recommend that you never buy a Pella window. They have been an absolute nightmare to own.
Review about: Pella Window.