Energy efficiency in buildings is a crucial factor in achieving global sustainability goals. Heating and cooling systems are the main demand process, and are necessary in all places, whether for heating up a building in a cold location or for cooling a building in a hot environment. Optimizing these systems is a good way of improving the energy efficiency of the buildings. In Sweden, district heating and cooling systems are widely implemented and constitute the dominant solution for thermal energy distribution in buildings. In contrast, in Spain, individual systems such as condensing boilers and split air conditioning units remain the most common technologies for heating and cooling. However, in recent years, increasing environmental awareness and stricter climate targets have driven the exploration of alternative systems, such as heat pumps and thermal storage solutions, as part of the transition towards more sustainable and energy-efficient buildings. The aim of this research is to analyse, through building energy simulation, the performance of heating and cooling systems in two contrasting climatic contexts: a cold location (Sweden) and a warm location (Spain). The objective is to assess the efficiency and environmental impact of different system configurations. First, each country’s typical system is evaluated in its native context. Then, a cross-application is simulated to observe how each system performs in the opposite climate. Finally, a common solution based on a heat pump coupled with borehole thermal energy storage (BTES), is introduced and analysed. This final scenario aims to explore the potential of more sustainable and efficient alternatives for future heating and cooling in the building sector.  Through detailed energy simulations performed with the IDA ICE software, key indicators such as monthly and annual energy demand, consumption per service (heating, cooling and domestic hot water), total energy cost and CO2 emissions are evaluated. The results obtained show that the system based on geothermal heat pump with borehole thermal energy storage allows a significant reduction in energy demand and greenhouse gas emissions in both countries. Although the initial implementation cost is high, the long-term operational savings and lower environmental impact reinforce its viability as a sustainable solution. The discussion also includes a preliminary analysis of the payback and the suitability of the system in terms of the climate and energy context of each country.