Ventilation systems in buildings have been traditionally designed for the maximum projected number of occupants; while buildings often have fewer occupants than the maximum and in some cases can be unoccupied for extended periods. Changing the rate of outdoor air to reflect changes in the number of occupants in a space is referred to as demand control ventilation (DCV). A field study was performed using thermal sensors to determine the number of occupants using lecture rooms of an institutional building. The occupant data was used to calculate minimum ventilation for the lecture rooms using current ventilation standards from ASHRAE Standard 62.1. It was found that by current standards, the required ventilation is considerably less than the original design ventilation. Based on occupant data and variables specific to the lecture rooms, it was found that the ventilation can be reduced by at least 40% creating a potential for significant energy savings.