In molecular dynamics simulations of heat transfer in micro channels, a lot of computation time is used when the wall molecules are explicitly simulated. To save computation time, implicit boundary conditions, such as the Maxwellconditions, can be used. With these boundary conditions, heat transfer is still a problem. In this work, we derive a new boundary condition based on a vibrating potential wall. The heat-transfer properties of the new boundary condition are shown to be comparable with those of the explicit wall. The computation time needed for the implicit boundary condition is very small compared with that needed for the explicit simulation.