Those kachelofens are pretty neat. I don’t understand why we don’t have them here in the US if they are so efficient at heating a home. I imagine you could build one yourself if you found a book on how to build them.
I did find a company in Talent, OR that sells them.
I also found a video of a kachelofen that can be retrofitted into an existing fireplace/chimney installation called Biofire (located in Ireland).
Biofire is a natural wood burning log stove with a glass or metal door. Using wood supplied locally enables it to be carbon neutral with minimum processing and transportation involved. Biofire is an ideal sustainable energy heating system for homes in Ireland. It is suitable for new and existing buildings. The Biofire (KACHELOFEN) clay brick oven gives a 90%~ efficient clean radiant heat all day from only an hour and a half of burning. This video is narrated showing a retro fit Biofire into an existing chimney breast. It contains an oven on the reverse side facing into the dining room. Three rooms are heated with an addition convection vent leading out into the hall transmitting heat further down the house. The fascinating visual demonstration of the Biofire is evident in the burn process as the energy embodied in the wood is released. Within the core of the Biofire the gasses are also burned in an 8M long flame instead of being released into the atmosphere. Less than 1% ash is all that remains with only a need for to clean out once or twice year.