In this learning track, we will learn about the Ansys Lumerical HEAT solver, which can be used for thermal simulations in the finite-element Multiphysics environment. We will start with the physics of the solver as well as its various modes of operation and discuss some real-world application examples for which the HEAT solver can be used. We will then set up and analyze the flow of heat in a thin film using the HEAT solver. Following this, we will cover useful information about various material models used by the HEAT solver. We will also introduce various simulation objects available in the HEAT solver, such as sources, monitors, and boundary conditions. Finally, we will discuss thermal-conductive and transient (time-dependent) simulations that can be performed using the HEAT solver.