Furthermore, buildings in practice often fail to deliver even the minimum ventilation rates required by current or previous building codes (e.g., of the 15 cross-sectional surveys included in Table 2, 10 surveys include buildings with ventilation rates below 2.5 Lsª1 per person). These low ventilation rates usually do not violate building codes and standards, which generally specify minimum rates for ventilation system design but not for system operation. New or revised building codes and standards may need to specify minimum ventilation rates during building occupancy to maintain acceptable levels of occupant health and satisfaction. Buildings with economizer cycle control systems have a minimum ventilation rate and increase the rate of ventilation above this minimum during mildweather. Changing the set point for minimum ventilation rate in these buildings will influence health symptoms during periods of low ventilation when the control system reduces the ventilation rates close to the minimum.