Estimate of evaporation rate from a partially wet surface using Schlünder’s analytical model is assessed from comparison with numerical simulations. The influence of pore shape and pore size heterogeneity is explored as well as the limit of the very low wet surface fractions. A modified form of Schlünder’s formula is proposed for the heterogeneous surfaces by using the pore influence surface areas obtained from a minimum distance surface tessellation technique. The modified formula provides a simple method for coupling the external transfer and the internal transfer in the pore network modeling of drying.