Well my garage is about 15x10 (maybe), and I am looking for a way to keep it warm in the winter. I was thinking about a rocket mass heater but I honestly am not worried about the mass parts that heats up and stays warm for a long time. I'm just looking to have it warm when I'm out there. Would it be useful to build the heater and just vent it out of my garage and not worry about the mass part? Would that work?
I think something along the lines of Peters barrel tower batch box would serve your needs well. A batch box would probably be better for you than a J tube, so you don't have to constantly fiddle with feeding and tending the J. Maybe 6" batch, with the extra barrel on top to dump tons of quick heat into the space. Maybe instead of the third barrel you could do a half-barrel bench seat for a nice warm seat to take a break during long projects.
The 8" batch box is almost certainly far too powerful for your workshop. I would think you can get away with a 6" version like I've used for one season in my former 18 x 32 ft workshop. See this link for description and pictures. Admittently, the ceiling need to be quite high to house this construction. And you do need a proper chimney to drive this heater. The workshop was larger than yours, but in the middle of a block of houses so the only outer walls were the narrow front and back. And in the Netherlands, not renowned for its harsh winters.
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