Furnace precision tune up; clean and tune up furnace; clean burners, test ignition components, adjust gas level, test safety circuit, check indoor motors, checked all electrical components, tested indoor air flow, checked heating temperatures, and tested overall furnace operation. Recommended a diamond screen on furnace exhaust termination. Recommended a surge protector to defend against electrical surges. Also, discussed the benefits of an electronic air cleaner. Customer declined recommendations at this time. Will follow up next week regarding the electronic air cleaner.