Do energy-efficient windows really save money?

They do, though the size of the savings depends on what you are replacing. Swapping old single-pane or failed double-pane windows for modern Low-E units can trim heating and cooling use noticeably in a climate like Chicagoland’s. The bigger everyday payoff is comfort: fewer drafts, warmer rooms in winter, and less strain on your furnace. Windows are a long-term investment, and the savings add up over the decades you own them.