Performed preventative maintenance for gas furnace. System is fairly old and from 1999. Inspected all the electrical components. Confirmed proper high and low voltages. Customers system should have a 16x25x1 filter not a 14x25x1. Saw a gap allowing dirt to flow through. Cleaned the burners, flame sensor and burner compartment. Performed a combustion analysis on the furnace. System is operating at 81.3% efficiency with a CO level of 25ppm. Tested the amp draw for the blower and inducer. Both are operating within the manufacturer specs but a little on the high side. Recommend updating the system in the near future due to age and condition. That being said system is operating properly at this time. Model #Kg6ra096c-16 Serial #Kg699158834