Demand side management (DSM) is known for generating synchronized behaviors of aggregated loads that can lead to large power fluctuations. In contrast to this well-studied occurrence, we report here on the emergence of novel synchronized behaviors of thermostatically-controlled electric heating systems in buildings with good thermal insulation and important solar radiation gains without DSM. To suppress the resulting large load fluctuations on the distribution grid we propose a centralized DSM algorithm that smoothens the total load curve - including electric heating and all other domestic appliances - of the cluster of dwellings it pilots. Setting up the baseline load is based on weather forecasts for a receding time-horizon covering the next 24 hours, while control actions are based on a priority list which is constructed from the current status of the dwellings. We show numerically that our DSM control scheme can be generically used to modify load curves of domestic households to achieve diverse goals such as minimizing electricity costs, peak shaving and valley filling.