The answer to 'how to maintain furnace' is to perform regular maintenance and cleaning to ensure your furnace operates efficiently and safely. This includes changing the air filter, cleaning the blower, and inspecting the heat exchanger and other components for any issues.
It's recommended to have your furnace serviced by a professional HVAC technician at least once a year, typically before the start of the heating season. They can perform a thorough inspection, clean the system, and make any necessary adjustments or repairs to keep your furnace running smoothly and safely.