Abstract The present work aims at analysing the thermal behaviour of the vapour flow inside the horizontal tube bundle of a cross-flow air condenser. It is pointed out that the steady-state air and water temperature distribution cannot be determined by means of analytical solutions, due to the non-linearuty of the problem. A model based on appropriate balance equations is introduced and a finite difference computer code is formulated. This code, which reports a large number of correlations found in the literature, is used to evaluate the different flow patterns that characterise the two-phase flow condensation. It is also employed to calculate the local heat transfer coefficient, for both air and water side, and the pressure drop on the water side. The main results, related to the evaluation of the condenser's thermal-hydraulic behaviour (pressure and temperature of the condensing fluid), are presented and discussed in detail.