Abstract: This invention relates to a novel tubular heat exchanger of the type subjected to hot gases and employs rappers to dislodge particulate material adhering to tubes of the exchanger. At least two parallel rows of serpentine tubes are positioned within a hot gas duct and are so arranged that the upper and lower loops define in a direction transverse to the rows of tube, parallel upper and lower loops. The rows are flexibly suspended at their upper ends. First knocker plates are positioned on opposed transverse faces of the upper loops and in a like manner, second knocker plates are positioned on the bottom loops. At least one rapping rod is positioned intermediate the upper and lower loops and extends between the tubes in the transverse direction. Raping of the tubes causes adjacent tubes to rap one another at their upper and lower loops. Relatively uniform rapping along the full vertical component of the tubes is achieved.