In this work, we study the conductance and the thermoelectric properties of a quantum dot embedded between two metallic leads with a side-coupled triple quantum dot molecule under a magnetic field. We focus on the spin polarization and thermoelectric quantities. Our results show the possibility of designing an efficient spin-filter device in addition to a noticeable enhancement of the Seebeck coefficient driven by the asymmetry in the quantum dot energy levels, and a tunable pure spin-Seebeck effect is obtained. This behavior also holds in the interacting case, where a pure spin-Seebeck effect can be obtained for fixed values of the embedded quantum dot energy level. Our findings could lead to the implementation of a new pure spin energy conversion and capable spin-filter devices working with weak magnetic fields.