A solid fuel heating apparatus (1) comprising a combustion chamber provided with a glass door (4) opening to the outside, an intake device (11) for the intake of outside combustion air into said chamber, an outlet duct for the burnt gases (2) and a sealed preheating enclosure for preheating the combustion air, conveying said air to the combustion chamber, connected at a first end to the intake device (11) and ending at a second end with a plurality of openings (9) releasing the air preheated by the preheating enclosure into the combustion chamber, characterized in that the preheating enclosure consists of a set of sealed heat exchanging pipes containing the combustion gases and the burnt gases (3, 8, 12, 15, 17, 18, 19), ending with the abovementioned openings (9), which are variable in size and are arranged in such a way as to modulate the flow of preheated air released into the chamber, enclosing the flame and combustion area in the natural conical shape of said chamber.