Unvented Heater Posted on 24th December 20153rd May 2021 by ThePD (The Project Definition) Unvented Heater is a vent-free combustion heating appliance, has no chimney vent that is located in the space being heated. Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window) Related Posted in Engineering and tagged equipment, heater, mechanical. ThePD (The Project Definition) ThePD has been developing the Preferred Project Definitions based on the actual project execution and operation experiences and knowledge with the Project Language, and sharing with you daily basis.