Generally, what is a sign of a furnace that should be replaced?

A furnace that is running inefficiently or is nearing the end of its operational life often shows signs such as rising energy bills. As furnaces age, their components may become less efficient, leading to increased fuel or electricity consumption to achieve the same level of heating. This increase in energy usage directly translates to higher monthly energy costs, which is a clear indication that the system may need to be evaluated for replacement.

In contrast, infrequent service calls typically suggest that the furnace is functioning well and efficiently. Similarly, the installation of a new thermostat might be part of routine maintenance or an upgrade but does not inherently indicate any issues with the furnace itself. Regular filter changes are a good practice for maintaining functionality and efficiency, but they do not imply that the furnace is nearing the end of its life. Therefore, rising energy bills serve as a critical indicator of a furnace that may require replacement due to potential inefficiencies.