Abstract: A chimney is disclosed having a plurality of blocks including corner positioned ambient air downflow passageways and upflow passageways surrounding a central combustion gas conduit. Ambient air flows downwardly then upwardly around the conduit to prevent over heating in the lower portions thereof and to maintain the upper portions at a sufficiently high temperature to preclude the condensation of creosote and the like. A unique cap construction vents the combustion products and heated air through separate openings and inducts cool ambient air for the downflow conduits through a covered opening provided by a cover cap assembly.