When window replacement is not the best option, you can tighten up old windows with weatherstripping
In New Orleans—and probably every other place in America—there hundreds if not thousands of historic windows and doors that can be weatherstripped rather than thrown away.
This short video shows how Bill Robinson's company, 504 Historic Windows prepares a window for weatherstripping.
To allow the sash to fit into the opening after the weatherstripping is installed, they trim the sashed 3/8 inch to 1/2 inch narrower than the window opening.
Cut an edge slot with a router along the jamb-sides of the sash. They also install weatherstripping at the bottom of the bottom sash, at the meeting rail of the bottom sash, and sometimes at the top of the top sash, so there is weatherstripping all around the window.
With the slots cut and sash trimmed, you can insert weatherstripping. Bill uses silicone bulb-type barbed weatherstripping at the top and bottom and nylon-jacketed neoprene strips (Q-Lon from Schlegel) on the jambs because the nylon stands up well to the friction of sliding the sash up and down.
In the video below, he explains his choices.