gm few days ago i came across this really old type of heater that is energy efficient (85-90%) and looks amazing (but are super heavy) Kachelofen (also tile stoves or ceramic stoves) or Masonry heaters these are similar to rocket stoves but masonry heaters release the heat gradually unlike conventional metal wood stoves which connect the chimney directly to the fire chamber, austrian masonry heaters have several meters of channels (commonly known as heat exchange channels or flue gas channels) separating the fire chamber and chimney connection. this separation allows for maximum efficiency by removing the highest possible amount of heat from the flue gases and storing it into the units high thermal mass before continuing into the chimney in canada they sell these as kits which can be self assembled