Improper window installation robs homeowners of the performance their products should deliver and that they paid for. A nationwide single- and multi-family building inspector estimated that 80% of problems with windows are associated with the installation.
The most important thing you can do to protect yourself is to insist on proof of training and certification. The most widely recognized certification is Installation Masters. Evidence of this certification will tell you that the window installer took the time to attend a two day, approximately $400 training and passed the exit exam.
Certification, along with visiting homes at which the installer previously replaced windows, should give you the confidence to move forward on this upgrade in your homes appearance and level of comfort.