a concrete slab forming a part of the building structure foundation is thermally insulated about its periphery from the ground upon which it resides from the ground surface to below the ground frost line , with the bottom of the slab in heat transfer relation to the ground below the frost line over a large part of the building structure surface area . the concrete slab directly overlies and is in thermal contact with an array of side abutting parallel rows of end abutting hollow cinder blocks to form air passageways for circulating air beneath the concrete slab and between the ground and the slab . by thermal siphon or forced air circulation , air , within the building structure transfers heat to and from the concrete slab , particularly heat entering glassed walls and impinging directly upon the surface of the concrete slab .