of total gas from the exhaust stack 4 thus measuring the actual percentage of oxygen concentration in the exhaust gas the analyzer 20 measures the amount of oxygen remaining after the carbon monoxide has substantially completely burned to carbon dioxide ideally this measurement will reflect the 50 excess oxygen supplied to the combustion chamber the oxygen analyzer 20 is in communication with an oxygen controller 22 and the oxygen controller 22 is in communication with the air control valve 14 the oxygen controller 22 may be set on a position reflecting the optimum percentage of free oxygen in the exhaust gas the optimum percentage of free oxygen in the exhasut gas is that concentration which at a given time reflects efficient conversion of carbon monoxide to carbon dioxide if the oxygen analyzer 20 measurement of the actual percentage concentration of oxygen in the exhaust gas is lower than the oxygen controller 22 setpoint reflecting the optimum concentration of oxygen in the exhaust gas the controller 22 will signal the air control valve 14 to open and admit sufficient secondary air to the combustion chamber 2 and vice versa thus the amount of secondary air is constantly varied in order for the actual concentration of oxygen in the exhaust gas to approximate the optimum concentration of oxygen in the exhaust gas in the control technique of the present invention the position of the oxygen controller 22 is a function of the percentage concentration of carbon monoxide in the waste gas therefore a carbon monoxide analyzer 24 is provided to.