Effect of dragged magnetic field lines into RAFM steel blanket modules on first wall heat load

•The magnetic field made by the blanket modules of DEMO as the ferromagnetic wall is calculated.•The effect of such magnetic field on the first wall heat load by the plasma heat flux is estimated.•The heat load becomes several times higher than the case of without the effect of ferromagnetic wall.•This result indicates that the effect of such magnetic field is not negligible and more detailed analysis is needed.