The answer to 'when to service furnace' is that you should service your furnace at least once a year, typically in the fall before the heating season starts. This helps ensure your furnace is running safely and efficiently all winter long.
Regular furnace maintenance includes cleaning or replacing the air filter, inspecting and cleaning the burners, checking the thermostat, and testing for proper airflow and carbon monoxide levels. Doing this annual service can help extend the life of your furnace and prevent costly breakdowns during the cold winter months.