My talk shall be concerned with the problem of rigorous derivation of the macroscopic laws governing heat propagation from the microscopic models formulated in statistical mechanics. A classical microscopic model of the thermal energy transport is provided by a chain of coupled oscillators on the integer lattice, that describes atoms (or molecules) in a crystal. Establishing, in a mathematical precise way, such laws, by taking appropriate scaling limits, is the central problem of rigorous statistical mechanics. One of the tools used to conclude such results is to introduce some stochasticity inside the system. We summarise some of the results obtained recently concerning the derivation of the macroscopic heat equation from the microscopic behaviour of a harmonic chain with a stochastic perturbation. We focus our attention on the emergence of macroscopic boundary conditions. The results have been obtained in collaboration with Joel Lebowitz, Stefano Olla and Marielle Simon.