The finite/infinite element approach provides the differential equation formulation of the unbounded engineering problems. Dipole-source-type problems with open boundaries have been treated accurately by means of mapped infinite elements. The mathematical procedure includes a simple mapping of the global infinite element into the local finite one. The influence of the number of nodes in mapped infinite elements on the accuracy of the numerical results is studied using a problem of a buried infinite cylinder with a given rate of a heat flow. Thus, the domain below the ground surface is handled combining the finite and the mapped infinite elements. The application of the 9-noded mapped infinite elements results in significantly more accurate numerical solution compared to the application of 6-noded element. Further increase of the number of nodes negligibly influences the solution accuracy. Consequently, the use of 9-noded mapped infinite elements is recommended for solving the unbounded dipole-source-type problems in engineering.