Podcast 266 – rocket mass heater shippable cores

Credit: Mike Ewing

Paul makes a spur of the moment podcast with Ernie Wisner about rocket mass heaters (RMHs). They are joined by Erica Wisner a little past the halfway mark.

Paul starts off with news that Erica's latest shipable cores attempt has cracked and they are now doing a post-mortem. Erica is now obsessed with creating the world's most awesome shippable core.

Paul's pebble-style RMH in the office has been getting mostly daily use for 3 weeks and is working well but they have some ideas for improvements. One thing they note is that it has a smaller mass than a typical cob RMH, so it warms up and cools down quicker. Maybe something more suitable for a weekend cabin, where a cob RMH would take too long to warm up. They talk about pocket rockets and how well they do what they do, which is radiant heating.

Ernie spoke about folks who complain that RMHs need a lot of tending (which they don't). Paul ascribed this to corporate trolls, but Ernie thinks it may have more to do with people who are used to L-tube rocket stoves assuming that rocket mass heaters (with J-tubes) suffer the same problem. Side discussions ensue about L-tube stove deficiencies and underhanded marketing tactics.

Paul brings the discussion back to talking about the working pebble-style RMH. Paul says they have removed the outer wooden box, having decided it is unnecessary. They also plan to add an external air intake. They talk about the merits and demerits of doing this. Ernie advocates having stoves that draw fresh air into the room rather than directly into the stove, but Paul wants to be able to leave the stove running untended and is concerned that without an external air intake, there's a risk of smoke coming in. Ernie appeals to people to note the circumstances when smokeback occurs and publicize these problems. Paul says that sometimes a puff of smoke will come out of the feed tube but be immediately sucked back in. Ernie adds that he is very familiar with his own stove and often leaves it burning untended without smoke or fire worries.

They talk some more about air intake design and how often people try to use steel for this. This is problematic because steel overheats even when it is quite far from the fire (probably due to radiant heat).

The discussion veers into high temperatures (2500 to 3000 deg. F.) and how steel and other materials deal with them. Paul notes that stoves with steel in the heat riser often burn out (and mentions a video by web4deb). Ernie says that the heat-riser design involving the inner and outer tube with perlite/clay mix between was not intended for long-term intallations because the heat riser is quite fragile after the metal is gone. He recommends brick for better durability.

Paul brings the discussion to the topic of people who want to get into the shippable core business. It seems the people who have contacted Paul with this intention do not, generally (or perhaps universally), see eye-to-eye with Paul on the value of the work he (and Ernie and Erica) have done and will do to make such a business succeed. The upshot is, Paul and the Wisners will be freely sharing their information on shipable cores. Their monetizing strategy is to allow others to take the information, get a business going and then, if the product meets with their approval Paul will list the product or business on Permies and take an affiliate fee for any sales through that channel, with an additional $20 per core going to Ernie and Erica.

Erica arrived at this point. Turns out that she knows a bit about these rocket mass heater thingies too!

They talk about the criteria that will be used to decide whether a core gets their approval. Paul says it must require minimal DIY skills to install. Ernie says it must burn clean. Paul points out that right now the box-style RMH has a shipable core (by freight) and this could already be the makings of a business. Erica's main criterion is that anybody newly exposed to a RMH built with the shippable core experiences an OMG reaction. She doesn't want a mediocre product at a cheaper price.

They talk a bit about the appeal of RMHs including the upside down fire.

Paul brings up another criterion, which is that the core must include the manifold (the transition area between the barrel and the ducting). There's more discussion of Paul's DIY simplicity criterion. Ernie objects that he'd rather have people learn more DIY skills, though he sees no harm in making the shippable core simple. He says he's seen the general level of DIY skill go down over time. Erica notes that its much easier now to develop skills because information is out there that used to be closely guarded trade secrets.

Ernie says he and Erica are looking for many more installers. They have a lot of clients lined up who would like a RMH installed. Right now they have somebody within 4 states of any potential clients, but would like to get it to within a half hour drive. Paul suggested a thread at Permies to list all those who are willing to build someone a RMH and where they are. Each of the people listed could also have a thread of their own with a gallery of their work.

Ernie says he will want the installers to follow the Wisners' plans on their installations. He also wants them to publicize any problems they encounter so they can address them. Erica says free answers are available in the regular Permies forum within 48 hours and faster answers are available for a consultation fee through Permies.com/consult.

Ernie sets Paul off by mentioning a particular incident and a short, rich (in f-bombs) discussion takes place about the appropriateness of customers wanting to know how you spend the money they give you.

Paul goes into a bit of detail about his preferred way to set up an affiliate program (with a 3rd party "money-fondler"). Erica brings up the low-toxicity of the refractory materials they are now using. They discuss embodied energy of the materials and Paul states that the savings of having a RMH easily outweigh this. He says he can't think of anything better to do for the environment than installing a RMH in a conventional home.

They talk a bit more about new versus existing homes. Paul said passive solar and wofati are definitely worthwhile for new construction. Erica recommends looking at pre-industrial homes for insights into how things can be done when considering new construction.

Paul starts wrapping the discussion up. Ernie messes up the tag-line just a bit.

You can discuss this podcast on this thread at Permies.

Relevant Links

Rocket stove forum

Get a personal consultation with Paul Weaton, Ernie & Erica Wisner and others

Ernie & Erica Wisner's website

Youtube video of a rocket mass heater autopsy

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