Urban development affects the urban microclimate (UMC) and, consequently, buildings' energy consumption patterns. Considering the urban heat island (UHI) effect in the energy simulation of buildings, especially regarding the uncertainty of future weather data, can support more accurate results and sustainable building designs. This study aimed to analyse the impact of urban microclimate on the energy consumption of an existing residential building in Auckland, New Zealand. The weather data was morphed using the Urban Weather Generator (UWG) and the data from an airport weather station. An existing building was simulated using the EnergyPlus simulation engine to examine the heating and cooling needs of a residential building under varying urban weather conditions and district characteristics. The inputs and assumptions were set based on the New Zealand energy code and available building documents and details. The results showed that the UHI effect has a noticeable impact on cooling demand in summer and heating demand in winter, with a difference of approximately 4.35% and 2.6%, respectively. The findings emphasise the role of urban morphology and characteristics in influencing local weather conditions, thereby highlighting the significance of urban design and arrangement in energy efficiency.