Expected lifespan is one of the main factors to consider when making replacement decisions about your furnace and AC. For example, if you think your functioning appliance will continue running for another 10 years, you’ll probably be less inclined to replace it. Furnaces typically last about twice as long as air conditioners, so they may still be going strong when your home’s AC unit gives out. On average: Furnaces can last around 20 to 30 years Air conditioners usually last around 10 to 15 years If your furnace is less than 10 years old when your AC quits, you may only want to replace the air conditioner. However, if your furnace stops working first, you may choose to replace both components because of the air conditioner’s shorter lifespan.