Is it worth replacing 20-year-old windows?

In most cases, yes. Windows from the late 1990s and early 2000s were often single-pane or early double-pane units with worn seals, and they leak far more heat than today’s models. Replacing them cuts drafts, quiets the house, and lowers energy use through Chicagoland’s cold months. If yours are fogging, sticking, or driving up your bills, that is your answer.