Biochemical exothermic reactions are continuously happening inside the human body. In order to prevent overheating of the body, it releases excess heat into the environment. If we put a human in a small room, we will, after a certain amount of time, notice the rise of temperature in this room. In my diploma thesis I studied how the temperature in room is changing, in the presence of human. A part of the experiments were performed in a small, realistic room, but most of the experiments were performed in a very small and isolated room. I found out that the rising of the temperature was faster in the beginning and gradually got slower. Many factors contribute to the warming of the room; initially most noticeable is the warming of the air in the room, later on the warming of objects inside the room and even later also warming of the walls. Differences occurred because of the different heat capacities of the materials in the room of the experiment. Furthermore the significant finding is that the human body does not warm up a room as simple as a heating device, which only gives off heat to the surrounding air, but is giving off most of heat by vaporization of the water from the body’s surface, as the temperature of the air is approaching the temperature of the body’s surface. The air of the room is not increasing in temperature but in humidity due to vaporization.