Abstract: The boiler has on the top thereof, a smoke discharging cover with a water receiving tank, the interior thereof includes an upper combustion chamber and a lower water storage chamber, a water storage tank is provided between the boiler wall and the combustion chamber in which there are a burner and a heat exchanger constructed by welding bundles of pipes on the bottom of a water collecting tray, many water chambers are formed by the partitions in the water collecting tray, the pipes communicate with the water chambers, further heat absorbing passageways are formed within the boiler wall and the smoke discharging cover, these can lengthen flowing time of water and enlarge area for heat exchange, rate of heat exchange and life of use of the heat exchanger are improved, dismounting of the heat exchanger for cleansing is also feasible.