If you are shopping for vinyl replacement windows, be sure they have been independently certified by the AAMA by looking for a label somewhere on the frame. The AAMA label is usually gold. It assures that the manufacturer has had their product tested for things like structural strength, resistance to air and water penetration, and verifies the energy efficiency  meets  or exceeds  energy star requirements. The AAMA does unannounced factory inspections to make sure the components used to make the window that was originally tested are the same components being used in production. To learn more about Vinyl windows and doors, visit my website at http://www.how-to-install-windows.com