The invention relates to a solid-fuel heating apparatus that includes a combustion chamber (1) and a first flue-gas discharge duct (6), characterized in that the heating apparatus includes: a dual wall (2A) defining a second flue-gas discharge duct (2) located outside the combustion chamber and on the flue gas path between the combustion chamber (1) and said first duct (6), and provided in a vertical section thereof with a plurality of controlled communication valves (11, 12, 13, 14, etc.) arranged at respectively different heights (h1, h2, h3, h4, etc.), the second flue-gas discharge duct (2) being adapted via an opening (2B) in the lower portion of the dual wall (2A) so as to extend the flow path of the flue gas by an amount depending on the selection of the open inlet valve in the second duct (2) while the others are closed; adjusting means adapted for selecting, for each of the valves (11, 12, 13, 14, etc.), an open or closed position based on the temperature of the flue gas measured by a temperature probe (7) located at said first duct (6) so as to adjust the length of the flow path of the flue gas (3) in order to minimize the temperature of the flue gas while maintaining the latter above the dew point thereof.