Heat Gain Posted on 15th November 20154th September 2020 by ThePD (The Project Definition) Heat Gain is the amount of heat transferred to building interior from all heat producing sources, mainly solar energy. 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 engineering, heat. 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.