8 inch rocket stove with a fan to increase evaporation give me 3 to 4 gallons per hour with one deep chaffeing tray. I built it out of stove pipe and perlite for a test run and burned it out in one season of use.
Any sufficiently advanced technology will be used as a cat toy. And this tiny ad contains a very small cat:
A rocket mass heater is the most sustainable way to heat a conventional home