Thermal management of machinery spaces of marine vessels using a heating ventilation and air conditioning (HVAC) system is needed to maintain the temperature within the tolerable limit for efficient combustion in internal combustion engines and proper functioning of on-board electronic devices by removing high heat generations from in-house auxiliary systems. This study presents a numerical methodology using coupled simple and detailed computational fluid dynamics (CFD) models of air passages and engine components. The developed method is found to have a good agreement with the experimental results. Further, different layouts of vents and heat-generating components in the engine room are analyzed to obtain air flow and temperature distributions. It is found that the locations of vents and heat generating components have a significant effect on the maximum temperature distribution in the engine room.