When financed with a long-term home equity loan, the money saved through reduced energy bills will often be less than the payment on the loan. Of course, new windows also have other non-tangible benefits, like ease of operation and improved appearance. You can also save energy and money just by weatherizing your windows. Caulking gaps around the frames and weatherstripping the sashes are relatively quick and inexpensive options for improving the energy efficiency of windows.
Storm windows can also be an effective approach.
Window shades and coverings can improve the energy efficiency of any window. Coverings now available incorporate thermal barriers such as reflective mylar films and slide on tracks that effectively seal the edges of the covering and resist air infiltration.