Performed preventative maintenance for 2 high efficiency furnaces. Replaced the 2-Merv 11 20x25x5 air filters. The humidifier services were done in the summer already at request of the customer so they are not needed to be serviced till next year. Inspected all the electrical components. Confirmed proper high and low voltages. Tested the amp draw for the inducers and blower motors. All are operating within the manufacturer specs. Performed a combustion analysis on the furnaces. The 1st floor system is operating at 93.5% efficiency with a CO level of 18ppm. The second floor system is operating at 94% efficiency with a CO level of 17ppm. Inspected the drains that we have had issues with both are draining properly at this time. Both systems are operating properly at this time.