  Thermal conductivity is one of the important mechanisms of heat transfer in
the solar corona. In the limit of strongly magnetized plasma, it is typically
modeled by Spitzer's expression where the heat flux is aligned with the
magnetic field. This paper describes the implementation of the heat conduction
into the code MANCHA3D with an aim of extending single-fluid MHD simulations
from the upper convection zone into the solar corona. Two different schemes to
model heat conduction are implemented: (1) a standard scheme where a parabolic
term is added to the energy equation, and (2) a scheme where the hyperbolic
heat flux equation is solved. The first scheme limits the time step due to the
explicit integration of a parabolic term, which makes the simulations
computationally expensive. The second scheme solves the limitations on the time
step by artificially limiting the heat conduction speed to computationally
manageable values. The validation of both schemes is carried out with standard
tests in one, two, and three spatial dimensions. Furthermore, we implement the
model for heat flux derived by Braginskii (1965) in its most general form, when
the expression for the heat flux depends on the ratio of the collisional to
cyclotron frequencies of the plasma, and, therefore on the magnetic field
strength. Additionally, our implementation takes into account the heat
conduction in parallel, perpendicular, and transverse directions, and provides
the contributions from ions and electrons separately. The model also
transitions smoothly between field-aligned conductivity and isotropic
conductivity for regions with a low or null magnetic field. Finally, we present
a two-dimensional test for heat conduction using realistic values of the solar
atmosphere where we prove the robustness of the two schemes implemented.
