Method for producing a series of at least a first and a second heat exchanger, each exchanger comprising: - at least one heat exchange matrix unit which comprises a successive stack of separator sheets and of corrugated fins delimiting a plurality of passages suited to allowing at least a first fluid, a second fluid and a third fluid to flow through the matrix unit, so that the third fluid can heat or be heated by the first and second fluids, each plate having a length and a width, the stack having a direction of stacking perpendicular to the length and to the width of the sheets, - the matrix unit comprising a predetermined number of openings which are each formed in a peripheral face of the matrix unit and which each communicate with one of the said associated passages, - at least one elongate fluid distribution tank (24, 42) which caps at least some of the openings, and which is connected to a pipe (30, 40), the axis of the tank being parallel to the direction of stacking and perpendicular to the width and to the length of the sheets, - the matrix unit or units of the first exchanger being substantially identical to that/those of the second exchanger, - the method consisting in adapting the exchangers of the series by installing several elongate fluid distribution tanks on the matrix unit, each tank capping just some of the openings assigned to the first fluid and to the second fluid, each tank having its axis in the direction of stacking, characterized in that each of the distribution tanks is connected to a pipe (30, 40) so that the number of openings assigned to the first fluid differs from the number of openings assigned to the first fluid, and for preference, the number of openings assigned to the second fluid differs from the number of openings assigned to the second fluid for the at least first and second exchangers of the series. - at least one heat exchange matrix unit which comprises a successive stack of separator sheets and of corrugated fins delimiting a plurality of passages suited to allowing at least a first fluid, a second fluid and a third fluid to flow through the matrix unit, so that the third fluid can heat or be heated by the first and second fluids, each plate having a length and a width, the stack having a direction of stacking perpendicular to the length and to the width of the sheets, - the matrix unit comprising a predetermined number of openings which are each formed in a peripheral face of the matrix unit and which each communicate with one of the said associated passages, - at least one elongate fluid distribution tank (24, 42) which caps at least some of the openings, and which is connected to a pipe (30, 40), the axis of the tank being parallel to the direction of stacking and perpendicular to the width and to the length of the sheets, - the matrix unit or units of the first exchanger being substantially identical to that/those of the second exchanger, - the method consisting in adapting the exchangers of the series by installing several elongate fluid distribution tanks on the matrix unit, each tank capping just some of the openings assigned to the first fluid and to the second fluid, each tank having its axis in the direction of stacking, characterized in that each of the distribution tanks is connected to a pipe (30, 40) so that the number of openings assigned to the first fluid differs from the number of openings assigned to the first fluid, and for preference, the number of openings assigned to the second fluid differs from the number of openings assigned to the second fluid for the at least first and second exchangers of the series.