  We study liquid-gas transitions of heat conduction systems in contact with
two heat baths under constant pressure in the linear response regime. On the
basis of local equilibrium thermodynamics, we propose an equality with a global
temperature, which determines the volume near the equilibrium liquid-gas
transition. We find that the formation of the liquid-gas interface is
accompanied by a discontinuous change in the volume when increasing the mean
temperature of the baths. A super-cooled gas near the interface is observed as
a stable steady state.
