  The fluctuations of the heat current in a quantum dot coupled to electron
reservoirs are calculated at finite frequency, voltage and temperature using
the nonequilibrium Green function technique. The non-symmetrized heat noise is
expressed as an integral on energy containing four contributions, each of which
includes transmission amplitudes, electron-hole pair distribution functions and
energy difference factors. The effect of the asymmetry of the couplings between
the quantum dot and the reservoirs is studied. Features of the heat noise are
highlighted and discussed for an equilibrium and an out-of-equilibrium quantum
dot. In the latter case and within the high transmission limit, the heat noise
is closely related to the radiative power spectrum, leading to an
out-of-equilibrium Planck's law. Proposals for the measurement of the heat
noise are discussed.
