Performed preventative maintenance for 2 gas furnaces. The main house system is a high efficiency furnace and the garage system is a standard efficiency ceiling hung unit. Inspected all the electrical components. Tested the amp draw of the blowers and inducers. All were operating within the manufacturer specs. Customer replaces the pure air kit for the main house system. The unit in the garage doesn't take a filter. Made sure all exhaust and drain fittings had tight screws due to some loosening from operation vibration. Performed a combustion analysis on the furnaces. Home system is operating at 94.6% efficiency with a CO level of 18ppm. Garage system had a heat rise of 85°. Basement system had a temp rise of 52°. Both systems are operating properly at this time.