Podcast 268 – Rocket Mass Heater Update Part 2

Credit: Mike Ewing

This is part two of a two part podcast in which Paul chats with Paco Wenzel, Zach Weiss, Derek Weiss, and Tony Ayuba, the folks who came out to work on the various winter rocket mass heater projects.

[0:00] Paul starts with an introduction of Zach, who Paul say IS Holzer agroecology - bringing Sepp in and working extensively with him and his people in Austria. Zach says he is Looking to get Sepp to come back in May, which Sepp has agreed to if his health is good. Either way, Zach will be organizing two trips to the Krameterhof this year at the end of July and early August.

Paul and Zach talk a bit about greenhouses, a subject they sometimes disagree on. This may be the topic for a future podcast. Paul admits that there are ways to make them suck less and that there may be things you can't grow in Montana without them (pineapple, guava).

[3:45] They talk about Erica's core in the auditorium's rocket mass heater, which Paul describes as a wierd little wooden box with metal at one end. Zach talks about a wooden door he has added as an experiment, but it's a bit difficult to follow exactly what he's describing. Paul has some fun with the word guillotine.

[8:50] Discussion of the auditorium rocket mass heater continues. Paul says its ducting is completely straight, i.e. no elbows until it gets outside. They've been doing a lot of experimenting with it, including trying to get an external pump working on the exhaust. There's difficulty with this because the mass is frozen, so the exhaust is coming out very cold. The auditorium RMH is a combination OF Erica's and Ernie's designs, with the core Erica cast and a manifold Ernie made from a half barrel and a ton of expensive aluminum tape. Sometimes it burns fine but sometimes not, filling the auditorium with flames and smoke. This requires opening the doors and losing all the accumulated heat, frustrating everybody.

[14:30] Paul describes Derek's idea of shortening the feed tube and feeding in half-sticks. This compensated for the heat riser in the RMH that is 6" too short and eliminated the smoke problem. Derek spent a full day splitting and cutting wood to a small size and feeding it to the RMH. The intent was to finally thaw out the mass and see if they could get the external pump working. However, the mass wasn't heating as expected. Even the manifold area was just warm. Using an instant-read thermometer, Paul found that the exhaust going into the mass was just 90 degrees. He took temperature readings down from the bottom of the barrel to the start of the ducting and observed a drop from 200 degrees down to 90 degrees where the exhaust enters the mass. So it looks like so much heat is being radiated by the barrel-and-a-half that there's very little left to heat the bench mass, and after a day at full burn they didn't get enough heat at the exit to test their secondary pump idea.

[20:20] Paul considered the possibility that an auditorium might not be the kind of space where a RMH's strengths are really most valuable. He's also thinking about putting insulation or cob on the lower half-barrel as a way to get more heat into the bench. He's not happy with all the tape used for the manifold and wants to move away from designs that require it.

[21:30] Paul revisits the heat riser problem and thinks the RMH might be fine if that flaw was fixed. They speculate that they could even add a foot or more to the heat riser, since the auditorium ceiling is 12' high. Paul goes back to the idea of cobbing the manifold so more heat goes into the mass. He emphasizes the importance of getting the secondary pump working on a pebble-based as a way to mitigate any leaks in the ducting.

[24:15] Paul talks about Erica's shippable (half)core from the previous workshop. Derek put a temporary Metalbestos heat riser on the core and fired it for 3 hours. Paul expected the weight to go down significantly since when the material used is fully cured it is as light as styrofoam. To Paul's frustration, it only lost a small amount of weight. He also said cracks started showing in the core, including a serious one. This has them all a bit worried.

[27:50] They are now adding chopped up graphite-impregnated door seal cord to the castings to make a composite that's less prone to cracking and this seems be an improvement. They have been casting rings out of this (they talk more about the rings at minute 38:00).

[30:25] Paul brings up the fact that the core, while they had the fire going in it had a really clean burn and very good draw, so he's very happy with that.

[31:15] Inside the house (mobile home) is another RMH, but it's a disaster. with a very bad draw. Paul lists some problems with it, including a slightly under-length heat riser, but is more concerned with the wood feed which is too tall and has steel in it. He says steel drinks in radiant heat and this, with the excess height, is turning the wood feed into a competing chimney. They've now taken all the metal out and plugged the external air intake coming through the floor, but have yet to test it again. They may ultimately rebuild the wood feed back up to the standard 16" or leave it short, as-is, and try burning short sticks in it as Derek did with the auditorium RMH to see how it goes.

[34:55] Paul switches topics to Tim's mold or cast. Tim is welding up a high-quality steel cast modeled after the cast core that was used in the teepee (this core fell apart). This cast will be industrial strength and highly reusable. They feel that once they've homed in on the right process and formulation for the casting mix, this cast will let them start cranking out good cores at a gratifyiing pace. Paul says he might also like to try using the cast with cobbish, a mix of clay, perlite & rock wool.

[38:00] Next, Paul starts dicussing rings. They are a way to bring the heat risers in the office and the auditorium up to the correct height. They are both about 6" too short. So Tim has cast two sets of rings. Each set is one large ring for raising the barrel and one small ring for extending the heat riser. They are being made with the mixture Erica developed for the castable core. They talk about the problems they've been encountering and learning from on the earlier attempts.

[41:40] Paul inserts some interesting trivia about the origins of Crisco.

[42:45] Paul now has about 50 metal folding chairs that came from the Sepp Holzer event in Boseman. Paul wants to make another mobile shelf like the others in the auditorium for these, but there's too much to do right now. For the time being, they are being stored in the shower.

[44:45] Paul praises the quietness of the electric vehicles, though he notes that their range is significantly smaller in cold weather. He also says they have three vehicles effectively offline, and that winter is normally the time for sorting out equipment problems, but they still have a bunch of other stuff they're trying to get done.

[49:05] Paul talks about how the Permies forums sort of scooped the dailyish email when it came to notifying people about the RMH Winter Projects event (the one giving rise to this podcast). Paul says the dailyish email is still probably your best bet, but you might want to keep your eye on Permies if you are interested in participating in a similar event in the future.

[51:10] Paul credits Deborah with coming out and doing most of the cooking during the event. Deborah is interested in having a tiny house and in heating it with a RMH. Paul talks about the 6" system that Ianto Evans had in his office and about aspect of putting a RMH in a tiny house (in this case, a mobile one). Paul warns that nobody yet seems to have made a 4" system that worked well.

[55:00] Paul brings up his final topic, which is auto-igniting propane torches. He has conflicting feelings about them. He feels as if he's cheating when he uses them, but they are sooo effective for getting a fire going. He compares using one of these to using a butane BBQ ligher (not so good) and a little butane torch he got off Amazon (works quite well).

[60:00] They wrap it up. Paul thanks all the participants and says they will probably be doing a few more of these until they get all their heating issues sorted out.

You can discuss this podcast on this thread at Permies.

Relevant Links

Rocket stove forum

Permies thread announcing the RMH winter projects event