Systems and methods are disclosed for ventilating a building using a rooftop heating ventilating and air conditioning system that in one instance involve determining a first outdoor airflow into the system through a barometric relief damper; subtracting the first outdoor airflow from a minimum required outdoor airflow rate to arrive at second outdoor airflow; and setting an outdoor damper to provide an outdoor airflow through the outdoor damper that is greater than or substantially equal to the second outdoor airflow. Other systems and methods are disclosed.