This paper focuses on the study of a solid/gas thermochemical reaction between a porous reactive bed and vapor. The objective is to determine the operating mode, either closed or open system, that best suits the requirements of a thermochemical seasonal storage applied to house heating. These two working modes have been compared thanks to two validated 2D models. This study shows that for the chosen set of parameters, the two operating modes lead to close global performances (the average specific power is 0.96 and 1.13 W/kg respectively for open and closed operating mode). Thus, the open thermochemical reactor, which presents technical advantages (easier conception and management, lower cost,...), is a promising way to implement a thermochemical process as long-term heat storage. Moreover, simulations allow identifying the main limitations for each working mode and the ways to reduce them. (C) 2014 Elsevier Ltd. All rights reserved.