The crystal and electronic structures, and the thermodynamic properties of Zr6X2Co (X=Al, Ga, Sn, As, Sb, Bi, Te) and Zr6Sn2T′ (T′=Fe, Co, Ni, Cu) ternary compounds in the Fe2P-type structure have been investigated by means of first principle calculations. The calculated structural parameters are in good agreement with the experimental data. The total electronic densities of states as well as the Bader charges of the atoms have been computed. Both electronic and size effects allow to explain the stability of the ternary Zr6X2Co (X=Al, Ga, Sn, As, Sb, Bi, Te) and Zr6Sn2T′ (T′=Fe, Co, Ni, Cu) compounds.