Performed annual 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. Discussed filtration of system with customer. Informed the filter currently in system is causing slight restriction on return air side. Unit is still within manufacture specifications, however even less restrictive filter will allow more airflow through system and into home.