We study the relation between the mean effective surface temperature (T) over bar (s) and the internal temperature T-b for magnetic neutron stars, assuming that the magnetic field near the surface has a small-scale structure. The heavy-element (iron) and light-element (accreted) heat-blanketing envelopes are considered, and the results are compared with the case of a dipole magnetic field. We argue that the difference in the T-b((T) over bar (s))-relation for different magnetic configurations is always much smaller than the possible difference caused by variations of the chemical composition in the envelope.