Besides being the main consumer of energy, buildings can be smart energy hubs offering demand side flexibility for the grid. The main loads in buildings are heating and cooling and they have the advantage to be flexible if controlled in a smart way. There are plenty of ways in which controllers can act for increasing the demand side energy flexibility of buildings and different approaches in quantifying and assessing it.This study uses a set of three existing key performance indicators to make a qualitative assessment on how the heating and cooling energy control is impacting indoor thermal comfort, the costs with energy and the self-consumption of the locally produced energy for a typical household located in different geographical conditions in Romania, under an electricity market design with a demand response program. The selected metrics are adapted for this analysis to allow a quick qualitative evaluation on how the building and its systems can reach the maximum achievable potential in terms of comfort, costs, and self-consumption. This approach can be applied both at design and operational phase. The results show that the participation in a demand response program does not influence negatively the indoor thermal comfort if constraints are imposed on these parameters, that the geography does not have a relevant impact upon the costs if a control technique dedicated for the participation in the demand response program is implemented and the participation in a demand response program does not influence the self-consumption.