Climate impact can be reduced by building energy efficient dwellings. Boverket, the National Board of Housing, Building and Planning, has under several years increased the requirements for new dwellings to reduce the energy consumption. During construction energy is used for material production, transports and others. However, the largest parts of the energy consumption of a building during its lifespan is used for heating and operations. Regulations issued by Boverket are designed as functional requirements. Thus, there are many different alternative ways the developer can design the overall building, the building envelope and technical installations to fulfil the requirements. The impact of climate on energy consumption in different parts of Sweden has been studied. The energy balance in a multi apartment building has been calculated manually and by computer simulations, using the energy calculation software VIP-Energy. Simulations has been done using climate data for four different Swedish cities, Malmö, Stockholm, Mora and Östersund. Different parameters for the buildings walls, windows, air tightness and heat recovery have been compared to analyse the impact on specific energy use. Results show that the building would meet the requirements with good margin in Mora and Östersund. Energy consumption can however increase by several percentage units at minor changes in the input data. A cost comparison for external walls with different U-values has been done, resulting in that the energy savings are in this case too small to justify the additional costs.