Technical research indicates that buildings can be used for short-term heat storage to peak-shave daily profiles in district heating. Increasing the energy flexibility of buildings implies new relations between demand and production – newly defined roles between residents and heating professionals. Heating professionals' understanding of residents is an important precondition for how these roles can be changed. To investigate this empirically, this paper reports from three future workshops where professionals from Danish district heating utilities, municipalities, energy companies and housing organisations discuss possibilities for including residents more actively in flexibility generation and more generally in district heating systems operation. The analysis focuses on the importance professionals ascribe to residents compared to other actors, the vocabulary professionals use to describe residents, and, most importantly, the rationales professionals ascribe to residents. Inspired by the notion of sociotechnical imaginaries, our analysis shows how the professionals imagine residents and ascribe rationales of autonomy, economy, comfort, involvement and sustainability to them. The professionals emphasise the first three rationales in particular. The conclusion points to the negative consequences such imaginaries may have for the future development of flexible district heating and proposes experimenting with various collaborative forms for engaging residents and professionals.