What would be the approximate O2 (oxygen) reading during combustion analysis?

In combustion analysis, the oxygen (O2) reading is an important indicator of the efficiency of the combustion process. Typically, for a properly functioning gas appliance, the excess oxygen levels can be quite low, indicating that the air-to-fuel ratio is close to optimal.

An oxygen reading of 3.0% suggests an efficient combustion process, where nearly all of the fuel is being consumed, and only a small amount of excess oxygen is present. This level is often indicative of a well-adjusted appliance that is operating efficiently, with little unburned fuel left and minimal excess oxygen.

As the options above indicate higher percentages of oxygen, those values are generally associated with either incomplete combustion or a richer fuel mixture, where more air is necessary for proper combustion, which does not reflect optimal performance. Understanding this allows for better tuning of appliances to ensure efficiency, safety, and environmental compliance.