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I am involved in a furnace replacement and tune up for energy efficiency program. The program has a standard that the CO level in the flue gas has to be lower than 100 ppm. I have a Rheem furnace that I can't seem to get lower than 130 ppm any ideas? The furnace is only 2 years old and if it does not pass it will have to be replaced. I already lowered the manifold gas pressure to 3" water column and I do not want to get that any lower than that. It is a single stage, two pipe direct vent system using approx. 12' intake and 12' exhaust through 2" sch 40 pipe.