Sectional heat exchanger for use in a heat cell

The invention discloses a sectional heat exchanger for a heat cell. The sectional heat exchanger comprises two end segments and one or more intermediate segment(s) provided between the two end segments. The one or more intermediate segment(s) and the two end segments are assembled in the heat exchanger. A combustion chamber is provided in the sectional heat exchanger, perpendicular to the one or more intermediate segment(s). Each of the one or more intermediate segments comprises at least one flow channel for a fluid to be heated. In between each two consecutive segments at least one flow channel for flue gas is present, which extends from at the combustion chamber. In between two segments, in the plane parallel with the one or more intermediate segment, the total width of the sectional heat exchanger decreases over at least part of the length in the direction away from the combustion chamber. The depth of the flow channels for flue gas, measured perpendicularly to the one or more intermediate segment(s) and