The trend toward minimizing ventilation of houses in order to reduce energy consumption for heating and cooling leads to an increase in indoor air pollution. The deterioration of indoor air quality (IAQ) negatively affects human health, safety, productivity and comfort. In order to evaluate the scale of this influence IAQ assessment has to be performed. However, the IAQ itself is not well defined and a number of parameters are considered as its indicators. In this work we compared carbon dioxide and volatile organic compounds as indicators of indoor air quality. In order to examine the problem, time series of CO2 concentrations were considered as the source of information about IAQ. The data were obtained from continuous measurements of CO2 and total volatile organic compounds (TVOCs). The following analytical instruments were applied: the non-dispersive infrared (NDIR) sensor- for CO2 measurements, the photoionization detector (PID) and semiconductor gas sensors -for TVOCs determination. The correlation and regression analysis were applied to examine the relationship between measured quantities in two time scales, namely one day and 30 minutes. They reflect different time scales of CO2 and volatile organic compounds (VOCs) concentration variation. Based on the analysis, we concluded that CO2 and TVOCs measurements conveyed different information about IAQ, as a function of time. The analytical method had strong influence on the information obtained. In particular, the discrepancy was observed when comparing NDIR and PID methods. Also techniques applied for VOCs measurements provided different information about these substances. The results of our work entitle to conclude that the total concentration of VOCs should be taken into account as the indicator of IAQ in addition to CO2.