Prevailing strategies to enhance the energy performance of existing buildings primarily emphasize comprehensive envelope retrofits and the replacement of energy systems. However, questions remain regarding whether these deep energy retrofits can achieve climate targets within the required timeframe and at affordable costs. Additionally, most studies prioritize system efficiency over sufficiency, often overlooking the significant role of occupants’ energy practices, particularly their heating habits, in shaping energy retrofit outcomes. This study explores incorporating heating practices into the retrofit decision making process of a Dutch terraced house. Using energy simulations, we evaluate the impact of retrofit packages on its energy performance. The analysis tested two levels of fabric quality—medium and high—to assess the performance differences across isolated measures and retrofit packages. Thermal loads were examined during the heating season, alongside initial investment costs of the retrofit packages. Findings revealed that reducing thermostat setpoints only can lead to energy saving of up to 44% during the heating season. Moreover, at lower indoor temperatures, where energy demands are already substantially reduced, the effectiveness of deep energy retrofit packages decreases, making the initial investment and effort difficult to justify.