Waste heat recovery is an indispensable solution towards high energy efficiency in various industrial processes. While many methods are available to recuperate waste heat of medium-to-high temperature range, limited solutions are applicable at low-temperature (<373 K). The present work presents a poten-tially reasonable cost while less understood method, namely the reactive heat transfer using reversible exo-/endothermic reactions for harvesting low-grade heat. Invoking high-fidelity direct numerical simu-lation, the interplay amongst turbulence, heat transfer, and chemical reactions is investigated in a heated channel flow. We consider a temperature difference between hot source and reacting working fluid of 100 K and show a remarkable improvement of heat transfer coefficient by 600% compared to non-reacting working fluid. This is associated with similar to 17% higher total energy absorption across the geometry of inter-est. These improvements are proven to be related to the existence of mild exothermic reactions near the channel core, the molar expansion, and the mild endothermic reaction close to the hot source which contributes to a thin thermal boundary layer, etc.