"Replacement window" installation involves replacing only the window’s existing sash and leaving the window frame intact. New window will be installed into the existing window frame. This economical option does not disturb the existing exterior and interior trims.
"New construction" installation involves completely removing the existing window and replacing it with a new one. With this option, you can easily change the function, performance and appearance of your entire window’s style. By doing this kind of installation you can easily repair rotten wood, improve insulation around windows and get more glass area. See attached picture HERE.