You don’t have to, but you should start thinking about your replacement plan. When furnaces die, they die fast, and a dead furnace in the middle of winter is no fun for anyone. Planning your replacement for a convenient time means you can ensure a new, functional furnace for cold weather. Plus, newer models operate more efficiently, so you’ll use less energy for the same amount of heat. Translation: A new furnace means lower energy bills. Until you’re ready to replace, keep up with annual maintenance and filter changes to keep your older furnace in good working order.