Hi there! I've spent the past few weeks reading through permies rocket heaters forums, but this is my first post--wish me luck!
Some folks & I are planning to build a heater in a tipi at an encampment started by a Native American tribe in New Jersey. The camp is standing in solidarity with Standing Rock and in resistance to a gas pipeline that is threatening the water and communities of the Northeast region. Campers will be staying in tipis and tents throughout the winter. They have some wood stoves but we want to experiment with a more energy efficient, DIY version. We don't have much money at all, so we are going for a version made primarily from salvaged and natural materials. That said, we can spend a little money on something that would improve the efficiency and longevity of the stove by a good factor!
I have some appropriate technology experience and have made small, low-tech, rocket cookstoves, but never any heating stoves. I really have tried to research quite a bit, but the information here is so copious and the diversity of styles so awesomely overwhelming that I hope it's alright for me to seek some specific advice on this thread
*Which style of heater?
> Ground as thermal mass
I think we don't have the time and space to do a large thermal mass rocket heater right now, e.g. one with a cob bench. The tipi designated to receive the first stove is on the small side. One thought is to dig the feed tube, burn tunnel, and combustion chamber into the ground a bit in the middle of the tipi, then run the exhaust from the 55 gallon barrel through the ground and out of the tipi, using the ground as thermal mass. I don't think we have money for the elbows that would enable us to run the pipe in a circle around the floor. So it would likely be a straight line of piping or salvaged steel round or square tubing, on a bed of rocks, maybe with some sand as insulation, and covered with soil. Does this seem like an okay idea? I myself worry that 1. Without insulating the ground inside the tipi from the ground outside, the capacity of the pipe to transfer heat to the ground might not be very effective, and 2. The area is low and I am told in certain seasons it can be a flood zone, which is obviously a larger problem...
> Radiant heater without mass
Considering this, I wonder if one of the models presented in the Aprovecho guide entitled "Designing Improved Wood Burning Heating Stoves (58 pages, October 2005)" (http://aprovecho.org/publications-3/
- scroll down to "Books") might be a better option. Specifically, the "Picasso Stove" presented on page 38 seems like a reasonable option. It's basically one barrel on top of another. The bottom part of the bottom barrel holds the fire on top of a grate. Above the fire there is a pipe surrounded by insulation and held up by a 'false floor.' This pipe feeds straight up into a second, equally sized metal drum, which serves as the heat exchanger and contains a smaller drum inside. The hot gases rise into the space between the smaller and larger drum of the heat exchanger and the leave via an exhaust pipe, which we would run out the top of the tipi where the smoke flaps are. (The manual actually recommends closing the space between the small and large drum, but leaving the smaller drum open so there is more surface area making contact with the air in the tipi.)
With the canvas tipi being generally poorly insulated as others on this thread have mentioned, what is recommended? Are the smoke flaps closed once there is an efficient heater that doesn't produce smoke? Is any kind of insulation or sealing added around the top? I was also thinking to hang a tarp on the inside, bottom half of the tipi. And perhaps hanging a blanket as an improvised ozan? From what I've researched this would cover the back of the tipi, behind the heater at the center. Any low-cost recommendations would be greatly appreciated.
At this point, I don't think we have time to build with cob and let it dry properly. So, we could use salvaged metal, but I have read that in a well-insulated, high temperature rocket-style stove the metal corrodes quickly. I'm thinking fire bricks sealed with mortar may be the best option. Though firebricks seem to be $1-1.50/piece in these parts. Vs. $8 for 2 feet of 6" diameter black stove pipe. Any recommendations considering a balance of cost effectiveness, heating efficiency, and eventual degradation would be greatly appreciated.
Thank you in advance for your patience and guidance!