The aim of this study is to investigate the temperature boundary layer around a human body in a quiescent indoor environment. The air temperature, mean in time and standard deviation of the temperature fluctuations around a breathing thermal manikin are examined in relation to the room temperature, body posture and human respiratory flow. To determine to what extent the experiments represent the realistic scenario, the additional experiments were performed with a real human subject. The results show that at a lower room air temperature (20 °C), the fluctuations of air temperature increased close to the surface of the body. The large standard deviation of air temperature fluctuations, up to 1.2 °C, was recorded in the region of the chest, and up to 2.9 °C when the exhalation was applied. The manikin leaned backwards increased the air temperature in the breathing zone, which was opposite from the forward body inclination. Exhalation through the mouth created a steady air temperature drop with increased distance from the mouth without disturbing the region of the chest. Exhalation through the nose did not affect the air temperature in front of the chest due to physics of the jets flow from the nose. The additional carbon dioxide (CO2) measurements showed that the exhaled air from the nose could penetrate the region below the chest. Small discrepancies between the results obtained with the breathing thermal manikin and a real human subject suggest that the manikin can be used for accurate measurements of occupant's thermal microenvironment.