A method of controlling exhaust air flow in an exhaust ventilation system including an exhaust hood, the method comprising: receiving, at a control module, an exhaust air temperature signal representing a temperature (Tex) of exhaust air in a vicinity of the exhaust hood (105, S410, S530), the exhaust air temperature signal being generated by an exhaust air temperature sensor; receiving, at the control module, a radiant temperature signal representing a temperature of a surface of a cooking appliance that generates the exhaust air (S420, S505), the radiant temperature signal being generated by a radiant temperature sensor; determining in the control module a state of the cooking appliance based on the received exhaust air temperature signal and received radiant temperature signal (S1112, S1118), wherein the determining further includes determining a fluctuation in the radiant temperature; and controlling the exhaust air flow rate in response to the determined appliance state by outputting a control signal from the control module (S1114, S1120), wherein the cooking appliance state includes a cooking state, an idle state and an off state, wherein the cooking appliance is determined to be in the cooking state when the fluctuation in the radiant temperature is determined and a mean radiant temperature is greater than a predetermined minimum radiant temperature (IRTmin, S1132), the cooking appliance is determined to be in the idle state when no fluctuation in the radiant temperature is determined, and the cooking appliance is determined to be in the off state when no fluctuation in the radiant temperature is determined and the mean radiant temperature is less than a predetermined minimum radiant temperature (IRTmin, S1146). receiving, at a control module, an exhaust air temperature signal representing a temperature (Tex) of exhaust air in a vicinity of the exhaust hood (105, S410, S530), the exhaust air temperature signal being generated by an exhaust air temperature sensor; receiving, at the control module, a radiant temperature signal representing a temperature of a surface of a cooking appliance that generates the exhaust air (S420, S505), the radiant temperature signal being generated by a radiant temperature sensor; determining in the control module a state of the cooking appliance based on the received exhaust air temperature signal and received radiant temperature signal (S1112, S1118), wherein the determining further includes determining a fluctuation in the radiant temperature; and controlling the exhaust air flow rate in response to the determined appliance state by outputting a control signal from the control module (S1114, S1120), wherein the cooking appliance state includes a cooking state, an idle state and an off state, wherein the cooking appliance is determined to be in the cooking state when the fluctuation in the radiant temperature is determined and a mean radiant temperature is greater than a predetermined minimum radiant temperature (IRTmin, S1132), the cooking appliance is determined to be in the idle state when no fluctuation in the radiant temperature is determined, and the cooking appliance is determined to be in the off state when no fluctuation in the radiant temperature is determined and the mean radiant temperature is less than a predetermined minimum radiant temperature (IRTmin, S1146).