This study investigates the potential of heat pumps in demand response (DR) programs, to provide flexibility to power grids with a focus on residential buildings in Belgium. The research highlights the interplay between grid flexibility, energy efficiency, and thermal comfort, presenting a multi-dimensional analysis of sustainable practices within the residential sector through analytical simulations and analysis of (3) case studies of demonstration projects in this research domain. Through strategic heat pump management, the study explores pathways for enhancing energy efficiency without significantly sacrificing occupants' thermal comfort. The core strategy of this work relies on the utilization of two distinct building types, with varying insulation levels defined by Belgian building standards as K15 and K45, each with a 180m2 floor area, as the backdrop for the investigation. These buildings are equipped with aero-thermal heat pumps that supply either radiators or a floor heating system and the building insulation serve as a proxy for thermal mass storage. The uniqueness of the study is embedded in the deployment of a genetic algorithm that optimizes the heat pump operations according to day-ahead pricing signals. In a winter scenario set for February 2022, the findings reveal a 13% difference in heating energy demand between the two building types, attributable to their different insulation levels. The genetic algorithm's application brought about notable cost savings, reducing peak demand by 28.56% for the K45 building and 14.52% for the K15 building. Flexibility is quantified in terms of heat pump consumption shifted away from peak demand periods. These numbers highlight the benefits of strategic heat pump operation and reflect the potential of DR programs to shift substantial energy demand from peak to off-peak periods