Completed furnace, maintenance and inspection. I cleaned flame sensor and wiped down furnace. I checked amp drawers and components. I tested airflow, temp splits, and humidifier. I inspected heat exchanger and tested for carbon monoxide. I detected 7 ppm coming from the furnace. I ran a combustion analyzer test on the system as well and furnace passed at this time. Furnace is operational and departure. I talked with customer about the carbon monoxide detector that was down in the basement bedroom. The carbon monoxide detector only sounds an alarm above 400 ppm and needs to hold that between 4 to 15 minutes. I told customer the best ones to get are low detection, carbon monoxide detectors. Customer will order some. Thank you for having us out today. It was a pleasure meeting you. Thank you for the gift and the cookies.