Meeting Passive House criteria for certification necessitates the HVAC engineer adopt a holistic view of design and embrace an integrative design process. Drivers for passive buildings are a function of the building geometry and the building enclosure. When the HVAC engineer understands the key elements of PH enclosures including the thermal and air barriers, windows and thermal bridging, the appropriate HVAC system will be notably different than traditional HVAC solutions. As engineer-of-record for dozens of large passive projects Petersen will answer the fundamental questions about how the approach of the HVAC engineer is different, and what the impact is on HVAC systems. How is the design process different? The engineer is a participant in reducing heating and cooling requirements for example, by advising the team on what enhances the thermal barrier and what compromises the thermal barrier, by understanding the impact of building geometry, window wall ratio, air-tightness, and thermal bridging. Once feasibility of meeting Passive House four criteria for heating and cooling is established, then HVAC system selection and design that responds to the enclosure performance can occur. What are some of the impacts on HVAC systems? Peak heat loss and heat gain in a PH building are dramatically reduced. The peak loads are well lower than most HVAC engineers have previously seen. Systems for heating and cooling in turn can be significantly downsized and simplified while providing superior occupant comfort. Dedicated outside air systems (DOAS) ventilation systems are carefully designed to provide outside air to all occupied spaces and exhaust an equal amount as supplied via exhaust from sources of odor, contaminants and toxins (in multi-family this is primarily bathrooms and kitchens). More complex systems such as perimeter heat, radiant floors, reheat and sophisticated controls are not necessary in passive house buildings for achieving comfort.