In this work, a mixed integer linear programming (MIP) approach for the optimal design of energy systems in residential buildings is presented. The optimization model considers the economic criteria of the guideline VDI 2067. The objective of the MIP is to minimize the annual costs which comprise the investment as well as demand- and operation-related costs. Conventional boilers, electrical heaters, combined heat and power (CHP) units, heat pumps (HPs), photovoltaic (PV) systems and thermal storages as well as local heating networks (HNs) are defined as options. The investigation on a building level shows that a boiler is the economically optimal solution for small buildings, followed by a HP unit. In multi-family buildings, both boilers and CHP units hold an economical advantage over HPs. For apartment buildings, CHP is identified as the economically optimal system. In the neighbourhood analysis of six buildings, the solver establishes a local HN which allows for both economical and CO 2 -emission reductions.