Room calorimeters are an invaluable, powerful tool in metabolic research studies. By using indirect calorimetry the research possibilities increase immensely in a wide range of clinical and research settings. These systems allow long term measurements (up to 7 days), without the limitations of a canopy or a face mask. They allow researchers to gain new insights in the dynamics of human energy expenditure, substrate oxidation and so much more. A room calorimeter allows studying a person’s energy metabolism over longer durations under different circumstances. The systems consist of three different parts: the room itself, climate/circulation control and an analysis unit: the Omnical metabolic system. Fresh air is pulled through the room and both the in- and outgoing air is analyzed. This allows free movement of the test subject in a highly controlled environment. Study duration can vary from 2 hours to over 7 days, while fully controlling the environment (temperature, humidity, light, etc), diet, circadian rhythm, exercise protocols etc. Additional equipment and sensors can be easily integrated to widen the possibilities even more.