HEAT is a simulation toolkit which combines plasma physics with engineering CAD to study heat fluxes on tokamak plasma facing components (PFCs). Recently, a runaway electron (RE) module has been added to HEAT for the study of RE impacts and the resulting PFC damage. This module builds on the existing functionality of HEAT including field line tracing and PFC intersection finding, but adds relativistic effects and drifts to better capture RE dynamics. In this work, simulations using the RE module in HEAT are shown. An Alcator C-Mod discharge in which start-up REs melted a diagnostic cable is simulated. Comparisons between experimental results and simulations are used to validate the HEAT RE module. In addition, HEAT simulations of various SPARC scenarios are shown. RE diffusion due to drifts during ramp-up is studied to assess the measurability of REs during this phase. It is shown that drift diffusion is dominated by high energy electrons and that early ramp-up detection is essential. In addition, HEAT is used to study a vertical displacement event and the relevant heat fluxes on PFCs. It is shown that this scenario in combination with an unmitigated RE beam is likely to cause melting. This work is supported in part by Commonwealth Fusion Systems.