  Within the framework of macroscopic quantum electrodynamics and scattering
theory, we derive the general expressions for the variance of radiative heat
transfer between two arbitrarily shaped objects placed in an arbitrary
environment in terms of their T-operators. The such derived expression is valid
in the far- and near-field regime of thermal radiation as well as for
reciprocal and non-reciprocal objects of any size within a reciprocal or
non-reciprocal environment as long as the distances between the objects and
their sizes are covered by the macroscopic approach. As special cases we
discuss the variance of the radiative heat flux between two nanoparticles and
between a nanoparticle and a substrate in near- and far-field regime.
