In Denmark, the penetration of Renewable Energy Sources (RES) has increased from 44% in 2015 to 55% in 2020 and is scheduled to increase up to 100% by 2050. To overcome the intermittency and volatility of the RES, demand-side flexibility is an alternative solution for the Danish Electricity Market (DEM). In the residential sector, the heat pump is a practical solution to hedge against the supply-side uncertainties associated with RES. To fulfill the aim, this paper suggests a novel hierarchical structure for residential heat pumps to provide power system flexibility. An Economic Model Predictive Control (EMPC) is proposed to unlock the heat flexibility of residential buildings in response to RES availability. The three-stage stochastic programming is addressed to schedule, adjust, and regulate the heat flexibilities of buildings hierarchically in three trading floors of short-term electricity markets, including day-ahead, intraday, and balancing market floors, on long, mid, and short advance notices, respectively. Leveraging heat flexibility based on occupancy patterns, the thermal dynamics of buildings are developed to address different temperature zones in residential buildings. Finally, a Danish Test House with 4 temperature zones is simulated to show the applicability and proficiency of the suggested approach. The results confirm that the proposed approach not only provides flexibility to the DEM but also reduces the energy consumption cost of households.