The current design and performance evaluation methods for vent and reflux condensers include minimum safety factors of 30% or more. These oversized condensers incur high capital and operational costs. Experimental data are fundamental in order to evaluate these design methodologies. This paper presents a new set of experiments performed in a steam/air vent condenser at subatmospheric pressures. The experimental apparatus consists of a vertical, double-pipe condenser with a length of 3 m and inner diameter of 0.028 m. The produced experimental data allow the evaluation of the local heat transfer coefficients and the heat-flux profile on the coolant side. After comparing the predictions of the two main methods for the design of vent and reflux condensers, that is, the film method and the equilibrium method as modified by Webb et al. (1996), it becomes apparent that the film method is always better and should be always preferred when diffusive data are available. The equilibrium method error in predicting the heat transfer area is shown to be a function of the Lewis number. Further valuable observations are noted regarding the calculation procedures of the two mentioned methods and the risks of using the equilibrium method.