Napoleon Ducted Heat ManagementNapoleon Ducted Heat Management Ducted Heat Management (DHM) is a system for managing the heat produced by the appliance at and around the fireplace. The purpose of DHM is to move the heat away from the fireplace to allow it to circulate more effectively with the living space. Benefits: Heat is circulated more consistently throughout the living space increasing comfort in front of the fireplace.* Increasing "real world" efficiency as heat is moved