The object of this paper is to show how the monitoring of key IAQ parameters can provide feedback on building performance in the areas of ventilation and airtightness. The availability of this information can then lead to the more effective operation of the building and its HVAC system because the operators will have better information on system operation. The monitoring of carbon dioxide (CO₂) concentrations, for instance, provides feedback on many aspects of HVAC performance, especially ventilation. Feedback on ventilation performance includes information on the adequacy of ventilation, the uniformity of ventilation, and the effectiveness of the overnight purge. Coupled with the monitoring of humidity, feedback on airtightness and energy efficiency also becomes available. The monitoring of multiple parameters of the indoor environment at strategically selected multiple locations in buildings, therefore, can provide important information on HVAC performance. As such, it can improve the management of buildings by reducing the amount of uncertainty in this performance. The better the operators know what the HVAC system is doing, the better they can optimize its performance for both ventilation adequacy and minimum energy use.