Abstract: A sectional heat exchanger for a condensing heat cell comprises two end segments and one or more than one intermediate segment(s). The one or the more than one intermediate segment(s) and the two end segments are assembled in the heat exchanger. A combustion chamber is provided in the sectional heat exchanger. Each of the one or the more than one intermediate segment(s) comprises at least one water flow channel for water to be heated. Between each two consecutive segments at least one flue gas flow channel is provided, extending from the combustion chamber. The one or the more than one intermediate segment(s) each comprise a horizontal row of ribs extending into the flue gas flow channel in order to increase heat exchange from the flue gas to the water to be heated. Ribs at the two outer sides of the horizontal row of ribs have a larger height than ribs in the middle of the row of ribs. With height of the rib is meant the dimension of the rib in the vertical direction of the sectional heat exchanger.

Abstract: The heat exchanger comprises at least one gas flow channel, at least one water flow channel, and a metal wall delimiting the gas flow channel from the water flow channel. The at least one water flow channel comprises a number of consecutive parallel straight segments. Two consecutive parallel straight segments are separated by a wall and by a U-turn comprising an upstream section and a downstream section. The upstream and the downstream sections are defined as the sections of the U-turn delimited on the one hand by the plane of the wall separating the two consecutive parallel straight segments; and on the other hand by the plane through the end section of the wall separating the two consecutive parallel straight segments, the plane which is parallel with the width direction of the water flow channel and which is perpendicular to the plane of the wall separating the two consecutive parallel straight segments.

Abstract: The heat exchanger comprises at least one gas flow channel, at least one water flow channel, and a metal wall delimiting the gas flow channel from the water flow channel. The at least one water flow channel comprises a number of consecutive parallel straight segments. Two consecutive parallel straight segments are separated by a wall and by a U-turn comprising an upstream section and a downstream section. The upstream and the downstream sections are defined as the sections of the U-turn delimited on the one hand by the plane of the wall separating the two consecutive parallel straight segments; and on the other hand by the plane through the end section of the wall separating the two consecutive parallel straight segments, the plane which is parallel with the width direction of the water flow channel and which is perpendicular to the plane of the wall separating the two consecutive parallel straight segments.