Fired heaters are used considerably in the energy-related industries and petroleum industries for heating crude oil in oil and gas sectors, refineries, DRI heater and iron ore industries. After realizing the fuel crisis and for being economical, researchers started thinking towards optimization of this process unit too. The aim of the simulation of Fired heater is to design the radiant and convection sections of heaters with consideration of multiple influencing factors. Along with, heat recovery from different sections of a fired heater and revamping possibilities to improve the heater efficiency, to reduce the flue gas temperature till the certain limit. There are a multiple influencing factors that affect the design of fired heater at the time of simulation like, type of coil, coil size, coil length, heater configuration, number of feed flow passes, a flow rate of feed and fuel type. In the present study, the comparison of simulation result on multiple influencing factors of same problem formulation in Cylindrical and Box type fired heater and discussion after changing the parameters by using the FRNC-5PC simulator.