I'm using ConductionTransferFunction and seeing the same "infinite storage" issue. https://unmethours.com/question/93625/infinite-heat-stored-in-ceiling/ https://drive.google.com/drive/folders/1n32Q6heH4L4tECSwKilm6UM3EvzYBSy5?usp=sharing

This seems to occur with and without PCM, with ConductionTransferFunciton AND ConductionFiniteDifference. It occurs for the drop ceiling surface, but not the roof surface. Perhaps the issue affects interior but not exterior surfaces?