I understand the need to keep it simple, starting with a basic rocket makes sense.
Be careful of using any fuel burning heater in an enclosed space.
A
carbon dioxide detector is cheap life insurance in such a circumstance.
I have been chewing on the idea of heating water for thermal mass, as a way to have an outside rocket stove heat my house.
I like idea of evaporating water and condensing it again, because the phase change embodies a huge amount of
energy, 8000 BTU's per gallon of water boilers into steam.
By contrast it only takes 1500 BTUs to bring a gallon of water from freezing to boiling.
For my own hoop house, I want to try boiling water into steam and blowing that hot vapor though perforated pipe, buried beneath the floor.
Another approach would be to boil water by the batch and let it drain into a old water heater, or even into the ground of the greenhouse.