Background <p>To address healthcare’s polluting environmental impacts, environmental sustainability is increasingly recognised as a key domain of healthcare quality improvement. Heating, ventilation, and air conditioning (HVAC) systems are important targets for environmental sustainability-oriented quality improvement, causing 70–90% of operating room (OR) energy consumption and incurring substantial amounts of greenhouse gas emissions. Safe and effective energy-saving measures exist yet are infrequently implemented in practice. This study aims to identify key implementation determinants for HVAC-related energy saving in the OR and to explore their prioritisation and interrelation.</p> Methods <p>We performed a two-phase sequential qualitative study in Dutch academic and general hospitals. Clinicians, engineers, managers, and infection prevention specialists with HVAC- and OR-related expertise were recruited using purposive sampling. First, we conducted semi-structured interviews based on the Consolidated Framework for Implementation Research. Findings were compiled into a shortlist of potential barriers and facilitators of implementation. Next, we performed combined ranking exercises and focus groups in different hospitals. Recordings were transcribed verbatim, coded by two researchers using a deductive-inductive approach, and analysed using Thematic Analysis. Ranking outcomes and focus group findings were combined to map key implementation determinants and processes.</p> Results <p>We included 42 participants, based on expert interviews (<i>n</i> = 12) and focus groups (<i>n</i> = 32, two overlapped) in five hospitals. Prioritised barriers were technical and organisational, linked to hospitals’ size and structure, adjustability of the current HVAC system, and availability of in-house expertise. Limited HVAC-related knowledge and equivocal beliefs regarding HVAC’s contribution to infection prevention shaped perceived feasibility of energy-saving measures and compatibility with OR workflows. Prioritised facilitators were the evidence base for energy-saving measures, organisations’ relative priority to save energy, and presence of a dedicated implementation lead. Both bottom-up and top-down approaches had initiated HVAC adjustment processes in studied hospitals.</p> Conclusions <p>Implementation of HVAC-related energy-saving measures in the OR is hampered by perceived implementation complexity, technical challenges, and individual knowledge gaps and beliefs. Dedicated multidisciplinary workgroups, managerial priority for energy saving, and collaboration of motivated individuals with complementary expertise and influence appear to support successful local implementation.</p>