A straightforward and general way for monitoring chemical reactions is via their thermal signature. Such approach requires however an experimental setup with a high thermal stability that simultaneously allows time-resolved heat detection with high sensitivity. We present a nanocalorimetric platform for accurate thermochemical studies of (bio-)chemical reactions in a miniaturized format (tens of microliter volume), characterized by a fast thermalization time to a preset temperature (<30 minutes), an excellent base temperature stability (±1 mK) and a fast sensing response time (few seconds). The platform is built around a commercial thermopile-based sensor chip, on which an open-well reservoir holding the sample is directly positioned. The sample is, prior to the experiment, pipetted into the reservoir, in which small aliquots of reagents are injected subsequently and sequentially via thermalized microfluidic conducts. The design of the platform is optimized by means of numerical simulations. Via thermoelectric calibration using a resistive heater positioned either on the sensor chip or in the reservoir, we obtain a maximum power sensitivity of 2.7 V W−1 and a heat limit of detection of 70 nW. The excellent functionality of the platform is demonstrated by measuring the reaction enthalpy of 1-propanol in water and the rate constant k and enthalpy change of the oxidation reaction of glucose catalyzed by glucose oxidase, showing good agreement with literature data. Our versatile platform may be applied to many thermochemical studies, including thermodynamic analysis and kinetic reaction analysis, and its ease of use will allow implementation of many different experimental protocols.