In this paper, the effect that the continuous curvature change of spiral heat exchangers has upon the size of these types of units is analyzed. For single phase and laminar flow applications, curvature, represented by the Dean number, strongly affects the heat transfer coefficient. In a spiral heat exchanger, curvature changes take place at every position along the length of the channels through which the fluids flow; so, in order to assess the effect of curvature on the final design, the heat transfer coefficient needs to be continually updated and a finite element design approach implemented. This approach is compared to a design methodology reported in the literature that uses average heat transfer coefficients. Results show that for laminar flow applications, in the case of designs with both fluids having equal heat capacity flow rate –balanced exchangers-, the difference between using average heat transfer coefficients and locally updated values is less significant compared to the case of unbalanced applications.