Validation of the created mathematical model was based on measurements of carbon dioxide concentration conducted in didactic room in two variants. The highest average deviation of the results of the carbon dioxide concentration from the simulations and measurements is 2.1% (room A) and 1.6% (room B).The deviation of the results obtained from the simulation and the results obtained during experimental tests is smaller than the total measurement error for a given test series. The study showed the versatility of the model. It gives an opportunity to apply for a description of the hygiene conditions in different types of rooms, used by different number of people in variable internal conditions (temperature, relative humidity, atmospheric pressure). The assumptions and simplifications of the model are its advantages, because make the model easy to use. Simulation of carbon dioxide concentration in closed rooms using a model can be useful to determine the time of mechanical ventilation switching on or to determine its efficiency. The model can be used in the design of air quality monitoring systems, including carbon dioxide sensors that control ventilation. It can also be useful for creating tools for counting people in a room.