The human body gets its energy input from food and gives an energy output in the form of mechanical work and heat. In the process, carbon dioxide and water vapour are released. In an experiment this process can be analysed in several ways. A person is placed in a thermally insulated box of a little more than 1 m3. The temperature, the relative humidity, the carbon dioxide concentration and the oxygen concentration are measured continuously by a data logger for 5 minutes. From the measurements you can analyse and calculate the thermal power of the body in several ways, taking into account the sensitive heat, the latent heat and the chemical energy released. The experiment can also be used as the basis for discussions on indoor air quality in e.g. a classroom and the global greenhouse effect.