SMOKE TUBE BOILER

The present invention relates to a smoke tube boiler including: a mix chamber which includes a mixing space in which combustion gas and air are mixed, a mix chamber body having a flat shape, and a flat plate-shaped burner disposed in a horizontal direction above a combustion chamber; and a heat exchanger which includes an outer shell forming an outer wall of a water tank into and from which a heat medium is introduced and discharged and which accommodates the heat medium, a plurality of tubes formed in a flat shape that are configured to allow combustion gas generated in the combustion chamber to flow therein and cause a heat exchange to occur between the combustion gas and the heat medium flowing outside the tubes, turbulators coupled to an inner side of the tube and configured to induce occurrence of a turbulent flow in the flow of the combustion gas, and multi-stage barriers disposed between the outer shell and the tube and configured to induce a heat medium flow direction to be alternately changed between a radially inward direction and a radially outward direction.