A system and method for calibrating flame current in a furnace is disclosed. The method includes initiating combustion within a combustion chamber by allowing flow of the fuel mixture to the combustion chamber; receiving, from a sensor, signals indicative of a flow rate of the air to the combustion chamber; receiving, from a flame rod sensor, signals indicative of a flame current of the combustion chamber; varying a flow rate of the air to the combustion chamber; receiving, from the flame rod sensor, responsive to varying flow rate of the air to the combustion chamber, signals indicative of a change in the flame current of the combustion chamber; and determining, based on varying flow rate of the air to the combustion chamber, and the change in flame current of the combustion chamber, a correlation between the flow rate of the air, and the flame current of the combustion chamber.