Abstract: The present disclosure is related to a structural improvement in the burning chamber of a horizontal boiler, adopting a hollow flame-conducting element therein, which is attached with a pair of parallelly spirally fixed heat-convecting fins for either increasing the heat-absorbing area subjected to the emitted flame from the flame-generating device or creating a whirlpool effect for the propagating flame so that the flame can come into contact with the wall of the burning chamber in a more ideal way and change its propagating direction more smoothly at the corner, resulting in an increase in the thermal efficiency of the boiler, in such a manner that energy consumption as well as a pollution problem can be alleviated greatly.