In the last part of this podcast, Paul and the innovators discuss the safer burn of the batch box. With this style and you can feel safer walking away just like a regular stove. This would have a door that would close and so you can have much more confidence leaving it alone. Ernie does make a point that it is still a rocket stove that one needs to be careful with.
Next Peter talks a little bit about a potential design for a rocket mass heater in a camper and then goes back to talking about his batch box. The system is designed to heat a large space very quick and this alone makes it safer because it is not on very long and because you are just fooling with it for a lesser amount of time.
They bring up some sort of debate they were having about the mass temperatures in one of the heaters they have at the labs. The temp at beginning and end of bench was 40 degrees different but at the beginning of the burn it is only 6 degrees different. So the mass isn't extracting the heat because the bench is missing for pebble style. It has no air intake at the bottom which is critical so they need to put the air ports in and test it again.
Paul mentions that they modified the shop so the exhaust goes through the roof and that he is the only one who wants it to go through the wall. Peter speaks for a while about the math calculations he did for this design. So basically what he has done is worked out a ratio of steel to masonry to convert one to the other.
The next thing they talk about is Ernie's heat pipes. It is a method of moving heat between stoves and a different mass or an application. They made them out of half inch copper pipe and a solder. It turns out they move heat really efficiently and could be quite game-changing for rocket mass heater design. It has to be at an angle going up in some fashion and it can successfully transfer heat 90 percent heat. It has one end in the flow and is be able to transfer it into a wall or into a radiator or into a hottub and heat the other materials. They talk about how why it isn't explody for a little while and Ernie says he wants to increase the pipe size. They finish up by talking about how this could effect solar ovens.
Next Tim talks about his Pocket Locket and Rocket. He explains that this was his attempt at something he always avoided which is doing too many things at once. It is a J tube hooked up to a griddle and then from there to an oven and then into a water heater. He talks about his black stove at home and describes that it was a 3.9 inch system but this is a recreation of a barrel oven that has been successful before. The real innovation is getting everything to gel and work together. He calls himself a junkologist so this project has a lot of miscellaneous parts. When they tested it, it was getting to about 400 degrees on the griddle and with with a baffle about 390 degrees. With the baffle completely down, it was 500 degrees. The oven temperatures were similar.
The water heating system he designed at PRI could heat about 50 showers a night but it means lifting 400 pounds of water about 3 feet so for this one needs to be modified accordingly. He talks about where the system is pressurized and it isn't a simple yes or no answer. They are heating the massive barrel of water and then dropping copper pipe in there and the copper pipe has the pressurized water in it. But it still needs to tested when this podcast was recorded so they don't know all of the details yet. This system is entirely mobile.
When asked what he would do differently he says he wants to make it easier to make and cheaper. He usually uses simple hand tools but he has done lots of welding with this one so he wants to change that. He also mentions a bypass would be a good system to heat the water up by itself.
When everyone was sending their materials lists Paul added materials for a 4 inch system for tiny houses and they were quite terrible and so Tim talks about a different idea that might work for a tiny house.
He says we should set up a hot water system outside of the caravan then do holes in the wall into some sort of radiating device. That way you get the benefit of the mass but you don't have the mass inside. It could be a car radiator with a thermosiphon pumping the water through the radiator.
Lastly they talk about Matt Walker's ring of fire. It is another outdoor space heater but it is more tuned to heat humans than it is for cooking It is a batch box with a big window. It is pretty much like Peter's system he mentions. Then it looks just like regular rocket mass heater and has the hole as well for cooking on top. And then they used half barrels for under the bench and did a full circle.
If you have questions or want to see pictures go to this thread. Paul also says they are thinking of doing a set of videos maybe because they have so much film coverage so he is thinking of doing another kickstarter in January for that.
Erica and Ernie mention they have their book almost ready. It will be called Rocket Mass Heater Builder's Guide and it deals with 8 inch systems. They have a 75 dollar bundle of is everything on their website and Erica mentions she will be doing pre-sales for their book and to be looking out for a thread about it on permies!
Credit: Cassie Langstraat
You can discuss this podcast on this thread at Permies.
podcast 413 – The problem with batch box rocket mass heaters – Part 1
podcast 403 – Bits and Bobs towards Critical Mass – part 2
podcast 402 – Bits and Bobs towards Critical Mass – part 1
podcast 398 – Review of Gracie’s Backyard – Part 2
podcast 397 – Review of Gracie’s Backyard – Part 1
387 – Wheaton Labs Goals – part 2
386 – Wheaton Labs Goals – part 1
385 – Uncle Mud – part 3