My first rocket stove sauna heater worked well for just over a dozen firings, and then crumbled. Too much water sprayed directly onto bricks. And the thing was badly designed, with an undersized chimney. In fact, I should never have called that unit a rocket stove. It was just a masonry stove, and an inept one at that!
After a few years of research and tinkering, and a few more builds of properly designed and built rocket thermal mass heaters, I arrived at version 2 of the sauna rocket engine. The stove could heat a warehouse. Instead it heats just less than 6 square meters!!!
System size is roughly a 20cm diameter, or an 8 incher. The sauna is up to temp in 25 minutes when the stove is run on full power. Thereafter I let it die down to about half power so that I don’t kill myself and whoever I have managed to lure into the oven with me.