We present imecSHE, a 3-D deterministic Boltzmann transport equation (BTE) solver for computing heat generation in realistic devices. Input-power-scaled Gaussian heat-generation profiles are shown to overestimate heating in the nanosheet-FET (NSFET) by an order of magnitude. Our simulations resolve the 3-D topology of heat generation and show that lowering the carrier effective mass can significantly reduce heating. Mobility-inferred effective mass is further employed to qualitatively study the channel reorientation effect on heat generation. Along the imec roadmap A14 → A3 scaling, p-FETs benefit the most with the heat-fraction (HF) dropping from 0.76% to 0.32%, while the n-FET HF is nearly unchanged. Finally, scaling studies identify actionable levers. Shorter channels and smaller drain size reduce heat. By providing physics-based heat-generation profiles in realistic 3-D devices instead of assumed heat sources, imecSHE enables quantitative optimization of device and process design to suppress heat generation for technology pathfinding.