To provide an improved heating furnace, in which ash is automatically poured to produce air spiral, in order to promote combustion of agricultural waste.

A heating furnace comprises a combustion chamber, a fuel supply apparatus, and a waste conduit. The combustion chamber includes an air outlet formed at an upper portion, and an opening formed in a base section. A fire floor is mounted over a base section opening for removing the ash from the combustion chamber. To the combustion chamber a fuel conduit and an air conduit are coupled. The fuel supply apparatus is mounted to an upper portion of the fuel conduit for feeding the fuel into the combustion chamber. A conduit for high-temperature air is communicated with the air outlet of the combustion chamber. Using such a heating furnace a whirl of fuel and whirl of air are formed in the combustion chamber. The fuel can be completely combusted, and the ash is automatically removed from the high temperature air due to the whirl of air. Combustion efficiency of the heating furnace is improved.