In recent years, 40% of the total world energy consumption and greenhouse gas emissions is because of buildings. Out of that 60% of building energy consumption is due to HVAC systems. Under current trends these values will increase in coming years. So, it is important to identify passive cooling or heating technologies to meet this need. The concept of thermal energy storage (TES), as noted by many authors, is a promising way to rectify indoor temperature fluctuations. Due to its high energy density and the use of latent energy, Phase Change Materials (PCMs) are an efficient choice to use as TES. A question that has not satisfactorily been addressed, however, is the optimum location of PCM. In other words, given a constant PCM mass, where is the best location for it in a building? This study addresses this question by positioning PCM to obtain maximum energy savings and peak time delay. This study is divided into two parts. The first is to find the best location for PCMs in buildings using EnergyPlus software. In this part, the mass of PCM used in each location remains unchanged. The second part involves the detailed study of the best location obtained earlier, mainly focusing on peak shift and peak intensity throughout the year. From the analysis, it is observed that the ceiling is the best location to install PCM for yielding maximum reduction in HVAC energy consumption for a hot, arid climate like Phoenix.