Abstract: A furnace heat exchanger tube cleaning apparatus is described. The furnace comprises a combustion chamber for generating heated gases including combustion products, a water jacket containing a liquid to be heated and including heat exchanger tubes passing therethrough and a flue for discharge of the combustion products. In operation, the heated gases including combustion products flow from the combustion chamber along the heat exchanger tubes to the flue. As the heated gases pass along the heat exchanger tubes, heat from the heated gases is transferred to the liquid in the container, thereby heating the liquid. The efficiency of heat transfer is increased by helical flights arranged to depend downward into the respective heat exchanger tubes from a support structure. Specifically, the flights create turbulence in the flow of the heated gases, thereby improving heat transfer.