The energy flow analysis in the building heating system alone can not provide sufficient thermodynamic insight of the different process involved mainly because it is unable to divulge quality content of the energy that limits application of energy conservation principle and therefore exergy analysis came in to picture, which provides more insight of each process involved and open up possibility of finding new source of renewable energies for sustainable buildings and likely optimization area in the system. The energy and exergy flow for a space heating systems of a typical residential building of natural ventilation system with different heat generation plants have been developed and compared. The aim of this comparison is to demonstrate which system leads to an efficient conversion and supply of energy/exergy within a building system.