I have a logwood boiler from marathon heater company. I am having difficulty getting used to the natural draft control (ammark control). I have not found the "sweet spot" yet . It seems that I have the fire roaring or it tapers down (not smoldering). I am currently burning seasoned wood (cherry/oak) but I may switch to coal. ($38 a ton in PA). The unit I have is the large on that can burn 36" logs by 10" diam. Overall I am happy with my purchase it burns long and hard. But I need to get this setup fine tuned.