A theoretical model is evaluated to investigate the characteristics of InAs/InP quantum dash (Qdash) lasers as a function of the stack number. The model is based on multimode carrier-photon rate equations and accounts for both inhomogeneous and homogeneous broadenings of the optical gain. The numerical results show a non monotonic increase in the threshold current density and a red shift in the lasing wavelength on increasing the stack number, which agrees well with reported experimental results. This observation may partly be attributed to an increase of inhomogeneity in the active region.