Performed preventative maintenance for Lennox high efficiency down flow furnace. Inspected all the electrical components. Confirmed proper high and low voltages. Cleaned the burners, flame sensor and burner compartment. Made sure trap and all tubing was clear. Customer replaces the Merv 11 air filter 16x25x4. Performed a combustion analysis on the furnace. System was operating at 92% efficiency with a CO level of 18ppm. Drained the drain trap of debris. System had a temperature rise of 54°. System is operating properly at this time. Recommend replacing electric water heater due to age in the near future. This is to prevent the chance of unexpected failure or water damage from tank starting to leak. Major corrosion on the inlet water pipe. Quote will be attached to replace water heater.