It may not make economic sense to replace all your windows (see Phil's tips for reducing heating costs), and you might want to keep the look of traditional windows. It is more cost-effective and better for the environment, in terms of producing less waste, to repair rather than replace older, historic windows. Another option is to have window inserts installed. They are quick and easy to put in place each fall and greatly reduce drafts and heating costs.
For more details, see this article:
https://www.treehugger.com/save-your-windows-and-your-money-indow-window-inserts-4858724