This study investigates the transient effects of heater on CO2 emissions in an automobile. In the evaluation of comfort in automobiles, in general temperature, humidity and air velocity measurements are taken. It is also important to assess the CO2 emission of the air inside a car. The aim of this study was to measure the CO2 emissions with different occupant numbers, different air velocities with different heating options. All experiments were carried out in a Fiat Albea 2005, during winter months. CO2 emissions and the air temperature values were measured from the breathing zone of the driver. It was observed that CO2 emissions increased rapidly in the first 10 min and stayed stable after 15 min for air-recirculation mode and CO2 emissions were significantly higher than that of air intake from the outside environment, which is 4.65 times of the air intake mode by mean values. Occupant numbers have effect on CO2 emissions, and two sedentary persons have 1.24 times greater CO2 emissions than that of one sedentary person without air-condition mode. Full heating period also affects the CO2 emissions in a car, and 20 min of heating period have 1.12 times greater CO2 emissions than that of 10 min of full heating period. It can be suggested that CO2 emissions must be accounted for the driving safety parameters in the cars. © 2011 Academic Journals.