Completed furnace, maintenance and inspection. I cleaned flame sensor and wiped down the furnace. I checked all components and amp draws. I tested airflow and temp splits. I changed out air filter. Furnace is running within manufacture specifications. Furnace is operational at departure. Today I recommended surge protection for the whole home and/or the HVAC system. I explained where those get installed and how it protects the systems. I also informed customer that the manufacturer could avoid the warranty if the system gets shorted out by a power surge.