This paper aims at providing sizing information concerning a thermal storage system in the case of a low energy consumption building (<50 kW h/m(2) y). Numerical simulations for a reference individual building were run for 23 different cities in Europe. Results show a clear correlation between annual heat demand Q(y) and annual heating degree-day (HDD): Q(y) = f(1)(HDD). There is also a good correlation between power demand and HDD. But as heat coverage of the entire heating period may be too ambitious, the analysis goes further. It presents a correlation between heating demand Q and HDD as a function of the storage system autonomy t of the form Q = (1 - exp(-t/tau)) x Q(y) with tau = f(2)(HDD). It also gives the absolute distribution of sorted power demand values as a function of HDD in the form of a power sizing chart. The purpose of this chart is to provide specifications for the sizing of a thermal storage system intended to partially cover energy needs and power demand of a low energy residential house. (C) 2013 Elsevier Ltd. All rights reserved.