A theoretical model using a heat and mass transfer analogy was developed to investigate the effects of noncondensable gases on the heat transfer coefficient of steam condensing inside a vertical tube. The Nusselt and Sherwood numbers in the gas phase were modified to incorporate the effects of condensate film roughness, suction, and developing flow. The model predictions showed good agreement with the experimental data obtained for various experimental conditions. A parametric study was conducted using the model with condenser tube diameter as a variable. The results indicated that the effects of noncondensable gases become weak as the inlet mixture Reynolds number (Remix,in = 4[over dot]mmix,in/dimix,in) increases and inlet noncondensable gas mass fraction (Wnc,in = [over dot]mnc,in/([over dot]mnc,in + [over dot]mv,in)) decreases. In addition, the effects of noncondensable gases also become weak as the condenser tube diameter decreases with the same inlet mixture Reynolds number because of interfacial shear stress.