"Exhaust ventilation is the norm in multifamily housing, but roof-top fans pulling air from multiple apartments leave many questions, including: - Does air actually get removed from all apartments? - If so, where does the makeup air come from? Sometimes air is intended to come from hallways, some packaged HVAC systems have outdoor air inlets, and sometimes builders install trickle vents to introduce outdoor air. How much air actually comes in through these pathways? A research project – including rigorous short- and long-term testing of pressures and airflow patterns in five new buildings – has attempted provide some answers. While there are still many questions, this session will present findings to date and recommendations for best practice. "