This research addresses the existing phenomenon in Eastern Europe related to office buildings heated by district heating. For enhanced heating efficiency, an office building is thermally insulated and/or run at a decreased space temperature. After that, in an office inside the building, the tenants may switch from district to less costly electricity heating due to the customary tariffs for district and electrical heating. The effects of this switch are analyzed by using software EnergyPlus. For the investigated office, it is found that a characteristic value of its heat consumption exists below which the heating switch decreases heating costs. In addition, the value of the heat consumption is recognized below which the heating switch also yields the decreased fossil fuel consumption and CO2 emission. For all cases, the consumed heat consumption, the consumed fossil energy, CO2 emission, and economic effects are recorded for heating devices in the excluded office. Furthermore, it is analyzed how these variables are influenced by heat transfer between the investigated office, and the adjacent offices. (c) 2012 Elsevier B.V. All rights reserved.