An analytic method is developed to describe the flow in each row of tubes of an air-cooled one-pass isothermal condenser. This leads to a better understanding of some common steam condenser problems, including freezing of condensate, rapid tube-side corrosion, and worse performance than predicted by any reasonable condensing coefficient. The NTU approach is used to derive expressions for pressure drop in each row in terms of exchanger effectiveness. The resulting simultaneous equations are solved numerically, and the solutions, presented graphically, show the flow pattern to be solely a function of effectiveness. For steam condensers contaminated by traces of air, it is found that air pockets will develop inside the tubes of the lower rows, blanketing the surface and preventing condensation. Several designs are described that attack the problem of noncondensable accumulation, including the most recent developments in the air-cooled condenser field.