A pinch design method for sequencing distillation columns in enthalpy flow rate / temperature (I/T) diagram has been compared with heuristic rules. Area between integrated columns has been investigated in connection with heat flows of columns and temperature differences in and between the columns. Heuristic methods for systematic synthesis of initial sequences of multicomponet separations can be explained with I/T diagram. Among heat integration combinations of columns structures with bigger intercolumn areas are better designs. The findings in connection with the heat integration were tested on an acetaldehyde process.