<p>The oven comprises a cylindrical main portion (27), a furnace (1) and a closed distribution system for combustion air. The primary air is introduced to the grate at the bottom of firebox and the secondary air is introduced through firebox door (22). The upper area of the furnace is inclined in the direction of the front portion of a flame rod (14). An air deflection plate (21) is arranged to guide the secondary air towards the glass pane (23) and to abduct the flue gas from the furnace into the flue gas space (15) between the plate and the rod. The tertiary air is introduced through a pipe (10) arranged at the back of the oven. A distribution channel (32) for tertiary air is arranged behind the firebox, at the back of the oven. The vertical rear wall of the furnace is arranged at various heights designed for inlet of tertiary air. The air introduction openings are formed in the lower region of the furnace main portion. The heat discharge openings (24) are formed in the upper region of the furnace main portion. The curved sidewalls of the furnace demarcate the fire chamber insert (12).</p>
