This paper investigates the importance of the design parameters when looking at possible energy savings and comfort enhancement in a building using Phase Change Materials (PCMs). Computer based simulations are performed using a simulation software for modelling a house and its thermal behaviour over a year. It is found that by varying the heating set point and the phase change (melting) temperature range of the PCM, significant changes can be observed. Some poor scenarios show that the integration of PCM can increase both the discomfort (up to 6% more discomfort hours) and the energy requirements (up to 25% more energy needed). On the other hand, appropriate scenarios bring significant energy savings (up to 33% less energy needed) and comfort enhancement (up to 31% less discomfort hours). This highlights the strong need for a clever design when integrating PCM into buildings. The goal is to find a trade-off between energy savings and comfort enhancement. The PCM with a phase change temperature range between 21 °C and 26 °C shows the best results. The study is based on climate conditions for Auckland City in New Zealand but most of the conclusions drawn can be applied to any climate. © 2015 Elsevier Ltd.