This study represents the pioneering application of the “immersed boundary method (IBM)” to the simulation of radiative heat transport in “complex geometries. Pseudo time stepping” was employed alongside the “finite volume technique (FVM)” to solve the “radiative transfer equation (RTE)”. Sharp forced interfaces were also used by IBM. This method was tested in both its two types of heat transmission modes: mixed radiant-conductive and pure reactive. The impact of the absorbent coefficient and various conduction-radiation characteristics upon the isomers and heat transfer concentration in a closed system with internal complex entities was then investigated. Results proved the method’s value in dealing with radiative heat transport problems in extremely non-trivial geometries. Given that the calculations for radiative transport and energies may be solved on either the Eulerian or the LaGrange grid, coupled heat transfer problems do not necessitate the use of a third grid.