||Fired equipment includes furnaces, fired heaters, fired boilers, supplementary fired boilers, and many other types of equipment. But for the purposes of reviewing how the calculations are accomplished and other factors that may affect the results of the modeling, we will use a fired reformer furnace as our example. All of the methods and issues discussed herein can be applied to any fired equipment. We will start with the combustion calculation which is necessary to calculate the properties of the flue gas, or the products of combustion as well as heat available from the combustion process. The chemical reaction formula for combustion is well known, but varies with the composition of the fuel being used, and can be very complicated if the fuel has many components. As an example, we look at a simple combustion of methane, CH4 in Oxygen, O2.