For natural draft equipment insert the probe for the combustion analyzer into the venting before the draft hood. For induced draft equipment insert the probe for the combustion analyzer into the venting a minimum of 12″ above the outlet of the inducer fan motor and before any dilution air. All readings should peak and stabilize within 5 minutes of startup and CO readings must be less than 100 PPM.
Often times a plugged heat exchanger or venting will cause excessively high CO in the flue.