Customer complaint: gas bills were higher than last year. I explained that the air conditioner is 50% more efficient, not the furnace. I fine tuned furnace using combustion analyzer. Stage one: manifold: 2.6 inches. Oxygen: 7.4%. CO: 42 ppm. Stack: 349. Supply air: 123. Return air: 69. Temperature rise: 54. Inducer: .08 A. Blower: 4.2 A. Stage two: timing: 12 minutes. manifold: 4.0 inches. Oxygen: 7.7%. CO: 29. Stack: 421. Supply air: 128. Return air: 69. Temperature rise: 59. Inducer: 0.22 A. Blower: 5.2 A.