When designing district heating serving different buildings, an architectural engineer should suggest optimal operation policy of heating, based on social aspects and on minimizing costs for used energy and for investment in building heaters. In this paper by using HTB2 software, the energy simulation was carried out for two small Serbian residential buildings with different heating timing (starting and ending time of heating). These buildings had different types of partitions: one with thermal insulation layer and one with bricklayer. It was found out that if heating starts later in the morning, the energy consumption in the both buildings may be lower and they may require smaller heaters. The thermal behavior of house does not depend on type of building partitions.