Abstract The “individual” accounting of thermal energy in household applications (heating, cooling, hot water) is a very essential tool for increasing energy efficiency of buildings equipped by central plants. Furthermore, the availability of real time energy consumptions data, typical of smart metering, enables users to identify the causes of any waste of energy and consequently to adopt adequate strategies to improve energy efficiency. Modern devices for thermal energy measurement and accounting are rarely present in historical buildings, despite energy consumptions are not negligible. In fact, historical buildings exhibit architectural constraints and plant configurations that strongly discourage the use of direct heat meters, both on a technical and economic point of view. This paper primarily deals with an in-depth analysis of thermal energy measurement devices for historical building applications. Furthermore, the authors show the results of a specific metrological analysis that enables both a comparison among the different options and the evaluation of the main criticalities about thermal energy measurements in historical buildings. The authors estimated typical uncertainties in heat accounting systems ranging from about 4.4% (direct heat meters) to 21.6% (insertion time counter compensated with degree-days). Intermediate performance for uncertainty has been estimated for heat cost allocators (about 9.2%) and for not compensated insertion time counters (about 13.4%), respectively.