Castle Build Masonry Heaters
Using chimney flue liners as both a structural and a thermal storage element, this style of heater breaks new ground in rocket mass heater design. There is no steel drum or cob bench. Instead of a horizontal flue for capturing heat, this design has one or two vertical bells.
This drawing shows the bells "unfolded" into a straight line so that it is easy to see how the exhaust moves through the chambers: