Fourier's second law was solved using convective boundary conditions without considering the shrinkage of the solid. The solutions for a finite and an infinite slab were compared to determine the dimensions for a slab to be considered as infinite. The solutions obtained for Bi = 0.1 and Bi = 100 correspond to heat and mass transfer-controlled processes, respectively, during drying. The results show that the finite slab cannot be considered as infinite, even for R2/R1> 20. The relative error obtained when the finite slab was assumed to be infinite was not significant for small Fourier numbers, but it increased as the Fourier number increased; errors were also higher for higher Biot numbers. When the numerical solution of a drying model was obtained for finite and infinite slabs, significant differences in drying kinetics and temperature evolution were observed.