[HayZee518]

Concrete block has voids or openings in the block. When placed together the openings sort of line up with the holes beneath and above it. You can pour vermiculite into these holes which will in effect insulate the block or take up the otherwise dead air space within the block. Once the inside heats up from radiated sunlight it will retain this heat for quite a while and in the winter convected heat from the room will keep the blocks warm, thereby eliminating condensate or lessening it on the outside surface.