Using this calculator, the heat load calculation is based on heating season, transferred heat to network, hours in a month, average outdoor temperature and total operating hours in a year at appropriate outdoor temperature. The main users of tool can be DH operators, DH engineers, urban planner and energy mangers in municipalities. Using this tool can be found the optimal capacities for an existing boiler house or the design for a new one. It also presents correlation between outdoor temperature and transferred heat to network. This information can be used to control the transferred heat and increase energy efficiency for DH companies.