1.1 This guide describes how measured values of indoor carbon dioxide (CO2) concentrations can be used in evaluations of indoor air quality and building ventilation. 1.2 This guide describes the determination of CO2 generation rates from people as a function of body size and level of physical activity. 1.3 This guide describes the experimentally-determined relationship between CO2 concentrations and the acceptability of a space in terms of human body odor. 1.4 This guide describes the following uses of indoor CO2 concentrations to evaluate building ventilation–mass balance analysis to determine the percent outdoor air intake at an air handler, the tracer gas decay technique to estimate whole building air change rates, and the constant injection tracer gas technique at equilibrium to estimate whole building air change rates. 1.5 This guide discusses the use of continuous monitoring of indoor and outdoor CO2 concentrations as a means of evaluating building ventilation and indoor air quality. 1.6 This guide discusses some concentration measurement issues, but it does not include or recommend a method for measuring CO2 concentrations.