There’s money to be made from replacing old windows, and sometimes a complete replacement makes sense for the homeowner, too, especially if the windows in question were never built to last. But in most cases, the hoped-for energy savings simply don’t justify the expense of tearing out and disposing of an otherwise sound wood sash. In my experience, any window that’s old enough to have weights and cords deserves an upgrade rather than a toss in the dumpster.Homeowners considering a window replacement almost always bring up energy concerns, but their bigger beef is that the units operate poorly — usually...