The hexagonal model of heat exchanger brick is well known, with its hexagonal or circular longitudinal inside channels and with a lateral profile selected so that when the bricks are placed next to one another they form other similar longitudinal channels, and by modifying the lower part of the brick in the shape of a step to reduce the outside dimensions, the outside vertical channels can be made to communicate horizontally. Such a brick having a "step" in the lower part of the brick is disclosed in Romanian patent 107441B. These bricks of the prior art have the follow disadvantages:
as a result of the presence of the step to reduce the horizontal cross-section in the lower part of the contour of the brick, the vertical lateral faces of the brick are complicated and therefore cause additional problems during molding, handling during fabrication and shipment from the point of view of uniformity and of the integrity of the additional edges created; PA1 because of the position and dimensions of said lateral step, the surface contact of the peripheral vertical faces of the brick with the thermal agent is limited to a reduced percentage of their size.