  We theoretically study heat transfer between two anisotropic nanoparticles in
vacuum, and derive closed expressions in terms of the anisotropic dipole
polarizabilities. We show that transfer between two small spheroids can be many
times as large as the one for two spheres of same volumes. Such increase with
anisotropy is also found for the heat emission of an isolated small spheroid.
Furthermore, we observe a strong dependence of transfer on the relative
orientation, yielding the interpretation as a heat transfer switch. The switch
quality, given as the ratio of transfer in the ``on'' and ``off'' positions, is
observed to be as large as $10^3$ in the near field and even larger in the far
field.
