we have just ripped out our fireplace and are gearing to install a new one…we have a new efficient insert that we would like to build a thermal mass around….does anyone know the math around building a masonry heater….do we have to know any tricks, of course we do…what i’m getting at is is it worth the effort to build a masonry “maze” for the heat to escape other than building in a straight chimney up….it is an efficient new insert that burns efficiently, whatever efficient is….i’ve seen some pictures of masonry that weaves around a bit before shooting upwards to trap more heat….thank you, michael hollihn, prana timber frames and sawing