Energy flexibility from residential buildings is foreseen as a solution to facilitate the integration of variable energy sources in the grid. In fact, the energy use in residential buildings is still high despite the different building regulations and some of their usages can be shifted in time. Among these usages, space heating showed an interesting potential for flexibility, especially in France, where 45% of the heating systems is electrical. The objective of this study is to evaluate the flexibility potential in typical French houses, looking at both the energy shifted and thermal comfort. Large differences are highlighted, mainly due to the thermal properties of the envelope and the type of emitter. The temperature drops are quick in poorly insulated building. Underfloor heating systems show a good flexibility potential due to the inertia of this type of emitter. Finally, quantitative data, such as the mean power decrease and power profiles, is provided to help the integration of flexible buildings in future energy grids.