  We study the electronic contribution to the thermal conductivity and the
thermopower of Weyl and Dirac semimetals using a semiclassical Boltzmann
approach. We investigate the effect of various relaxation processes including
disorder and interactions on the thermoelectric properties, and also consider
doping away from the Weyl or Dirac point. We find that the thermal conductivity
and thermopower have an interesting dependence on the chemical potential that
is characteristic of the linear electronic dispersion, and that the
electron-electron interactions modify the Lorenz number. For the interacting
system, we also use the Kubo formalism to obtain the transport coefficients. We
find exact agreement between the Kubo and Boltzmann approaches at high
temperatures. We also consider the effect of electric and magnetic fields on
the thermal conductivity in various orientations with respect to the
temperature gradient. Notably, when the temperature gradient and magnetic field
are parallel, we find a large contribution to the longitudinal thermal
conductivity that is quadratic in the magnetic field strength, similar to the
magnetic field dependence of the longitudinal electrical conductivity due to
the presence of the chiral anomaly when no thermal gradient is present.
