A furnace rarely quits without giving you warning signs first. The problem? Most homeowners don’t recognize the signs  until the system completely fails—usually during the first deep freeze of the year. Knowing the early indicators can save you from a cold house, an emergency repair bill, and the stress of a surprise breakdown. Here are the top 10 signs your furnace is on its last legs , and what you should do next. 1. Your Furnace Is 12–20 Years Old Most furnaces last 12–20