George, Heating equipment does not "tell" you when Co is being released
because of a cracked exchanger, poor draft or racoon in the chimney, I
had a racoon in my chimney.

Co detectors do. They save enough lives in Chicago that they are
mandatory in apartment buildings. The proved thenselves to me when the
exaust blower motor on my 117000 btu water heater failed. They should
be mandatory, Co does not smell and burnt NG can be decieving