Rocketstoves in all their forms are very interesting.
I built a
RocketStove Grill this summer. Fun to cook on.
A local energy group is currently building a "gasirockifier" - it is a combination of rocketstove and gasifier to be used as a boiler. The fire to water heat exchange area is double-walled, welded steel tubes, one inside the other. Essentially, it's a big water jacket.
I would think a drum-within-a-drum would be a simple way to create a rocketstove with water-heating capabilities.
Isn't a natural gas water heater just a big drum with a tube up the middle? I wonder if an old gas water heat COULD be easily modified into a rocket boiler?