Abstract: A heat exchange structure is constructed from refractory blocks having three linearly aligned flue-forming openings extending from top to bottom of the block. The central opening is surrounded on four sides by refractory and the two end openings are surrounded on three sides. These refractory shapes are assembled in an open basketweave structure to form the heat exchanger. The resulting structure contains vertically extending, interconnected flues of two types, (1) flues of a first type interconnected at alternate layers in the structure to each of the four contiguously adjacent flues and (2) flues of a second type connected to opposed pairs of contiguously adjacent flues at alternate levels and to the other pair of contiguously adjacent flues at the intermediate levels. The net result is a stable heat exchange structure with relatively thin walls, relatively large flues, and means for creating turbulence in gas passing through the exchanger, thus increasing the rate of heat exchange.