The answer to 'when to replace furnace' is that most furnaces last 15-20 years with proper maintenance. However, there are several signs that indicate it may be time to replace your furnace, such as frequent breakdowns, higher energy bills, inconsistent heating, and the furnace being over 15 years old. If your furnace is nearing the end of its lifespan or exhibiting any of these issues, it's a good idea to have a professional HVAC technician evaluate your system and provide recommendations.
Replacing an older, inefficient furnace can improve your home's comfort, reduce energy costs, and provide greater peace of mind. A new high-efficiency furnace can be a significant investment, but the long-term benefits often outweigh the upfront cost.