Episode-1243- Paul Wheaton on Rocket Mass Heating — 35 Comments

  1. Jack, Just curious, but how do you heat your house? Do you guys use wood heat or something else? Are you considering putting in an RMH? OR, how do RMHs fit into your homestead plan? You might have mentioned this somewhere, so if I just missed it, I apologize.

    I love your interviews with Paul… Have him on all the time!

    • Nvm… Just heard you say that in the winter you get enough heat you don’t really need one… I should listen to the WHOLE thing before I start firing off questions.

    • We have central air and heat. We just barely use the heat. We also have a HE wood stove, but it has not yet gotten cold enough ever for me to be willing to start a fire in it. The passive solar gain in this house is just so awesome in the winter it never really cools off much during cold nights until about say 3 am, then the heat kicks on for a little bit but not much.

  2. Thank god for this show!!!! I am literally building a rocket mass for the greenhouse as we speak…

  3. This was a great show. I love hearing what Paul has to say and you guys have an awesome way of interacting that keeps everything interesting. I’ve followed RMH for a while so I did not learn much in that area although I had not seen much on the pocket mass so that was new to me. I may try my hand at one of these this winter to set outside my little workshop as a warm up station. It’s been a while since I checked in on the WOFATI and it’s great to see the progress.

    Thanks for the show Jack.

  4. Always a pleasure to hear “The Crazy Guy From Montana”, especially when its here. I really enjoy how the two of you spark off each other while agreeing on the majority of issues. Great podcast, Jack!

  5. Thanks for this show. I hope to put a small “cabin” (okay it’ll be a tool shed) in Maine next year, and am considering whether this would be a good way to heat it. Would it be feasible to set up one of these heaters so it would not just heat but also cook on as well as maybe heat water? I was thinking if a bunch of tubes with water flowing through it next to it would be a good way of heating some water (aside from just putting a pot with water on top).

    Is this really safe to leave running and go to sleep, or exit the cabin while it burns out on its own? What about cats? I have visions of a cat igniting his fur, running around in a panic while on fire, and then setting everything else on fire. Does the flame need to be open or can it be covered? I also worry about a spark coming out, rising up to the roof and setting everything on fire.

  6. The problem I am having is trying to reconcile the designs and photos that I have seen online, and the design and look of our house. We have a traditional country farm house, and our main living area is on the second floor, with sleeping on the upper floor. The only place it really makes sense to have the RMH is in the living area, but we are talking about conventional wood flooring, plaster(ish) walls, etc. I don’t live in the cob, hand-sculpted home with no basement that seems to dominate all of the photos I have seen. Building a large, heavy thermal mass in my house makes me very uneasy from a structural engineering perspective. For Paul to make a statement like “RMH are currently the most sustainable heating source for conventional homes” seems, dare I say, “just marketing”? Anyone have any thoughts, suggestions?

    • I was wondering about the weight of all that thermal mass. I want to put this in a “tool shed” cabin, but built stronger than your average shed. No basement. Would that hold up? Also, I want a smaller version of it. A 55 gallon steel drum would take too much room, and be too hot.

    • I have not built a rmh yet but will be building one of his pebble versions I the next few months. I chose the pebble version for the fact of its “portability” and the fact that it would seem to be less weight. On a typical cob rmh I am guessing that the mass would be in the range of 1 to 2 tons in weight so for mw it is not an option (trailer home).
      You could make a pocket rocket heater and add a mass to that. Look at this page about half way down you will see a pic of a pocket rocket with stones around it held in place by a wire mesh.

  7. Do you have to be able to weld to make one of these? Can you use regular duct pipes or should you use fireplace duct? Is there a difference?
    I have seen a lot of videos online and listened to all of Paul’s podcasts, and people make it look so simple, but they also don’t go deep into the “how-to’s.” I have the book ( but have not read it cover-to-cover. Didn’t think I needed to.
    My original plan was to put one in my basement. Then I thought it may be safer to put one in my greenhouse, but after Paul’s safety warnings, I am now leaning towards making outdoor benches.
    Thanks for the show!

  8. This was a brilliant show which got me thinking about function stacking.
    Jack, I am curious if it would be possible to build a small compartment in the bed of the RMH large enough to accommodate a cast-iron camp oven. I imagine it would need to be lined with firebricks and a firebrick door so that it is hot enough inside to cook your food without melting your camp oven in the process. Has anyone previously done this? Any thoughts and suggestions would be appreciated.

  9. Excellent Show, as per usual.

    I don’t want to sound like a dick, I’m just intrigued, does anyone know how Paul Wheaton actually makes a living?

  10. SInce the book Paul refferenced is outdated, is there any way to see printed plans, etc… to build one ? I would love to see known, tested designs, when my wood stove burns out again, which is coming this year or next, I need to repalce with something.

    Also, here is a question for Paul. Is it more efficient to have a combo wood heat and cooking stove, or to go ahead and have one of each ? I live in California, in the mountains where it does get cold, but as I have tightened up the house, I do not need heat all the time, or always alot of it. Wood is our only heat source now and for all in my neighborhood. So, if I had 2, I could have something like an AGA wood cookstove, very well insulated, great for cooking, doesnt generally heat up the house much, in the kitchen. Then, build one of these inexpensive mass rocket stoves where the current wood stove is in the living room.

    The other option is to have one stove, like a heartland, for heat and cooking in the living room, with just a cheap stove in the kitchen for the odd moments where there is no sun and the wood stove isnt going and yo want tea….. Of course, it is less convenient to bring stuff further out to the front room to cook.

      • I must have missunderstood what he said in the interview. Or, maybe I’m saying it wrong, didnt he say that there is much more updated knowledge and design s since the book ? If I’ve missheard this, you can see why I need information in print and not just auditory

      • The book is currently eight years old. We’ve come a long ways since then. The book is now quite good at making several points – but really falls short in things like how the manifold is built. It also makes no mention of some of the newer materials that are being experimented with.

  11. Question for Paul.
    In the podcast you mentioned venting out a wall versus out the roof and said that you had a stove that did both with a shutoff to switch between the two. You then said that one way worked way better but didn’t say which way. By what you were saying though I got the impression that venting out the wall was worse.
    I will be making one of your portable or pebble versions this month and was planning to vent it out the wall so any info would be great.

  12. Question for Paul. Have you seen or tested the Dragon heater core? I’ve been to their site and it looks good but would like an expert to take it through a test before I shell out the cash to get one.

    • First, here is a simple thing you can make at home:

      I very much like the idea of supporting a product like the dragon stuff. When they first contacted me, I looked at their stuff and thought it fell short. I didn’t want to get into a four hour conversation about it, so I let it go. Later, we had a thread at permies about looking for somebody to take on this business and they publicly confronted me about not replying to their emails. So I asked about the riser construction: was that wood screws holding it together? What is their temperature rating? How do they prevent gasses leaking through the edges? They didn’t answer my questions.

      I like the idea that there are a dozen manufacturers of shippable cores and I can endorse my favorite.

  13. Paul,
    I am not a stove builder (yet) or a mason, I do heat with wood so I understand the desire to maximize heat gain and minimize smoke, soot, and wood use.

    regarding the Dragonheater: Their site claims a temperature rating of 2,600 F for the material , not the assembly. screws are “stainless steel”?

    They assembled on at a recent MotherEarthNews fair I attended.
    It looked similar to something I saw a few years back from the Masonry Heater Association built using clay flue liners. They have some beautiful heaters on their site ( )

    Do you think it would it be practicle using castable refractory cement, to cast a riser as one piece ( so no screws or seams to leak ) ? all I have seen cast are flat 1-2″ thick sections.

    I noticed that there is something called the “Wood Stove Decathlon” is occuring in DC on the mall (Nov 15th-19th). I was wondering if you had any favorites in that contest.

    • Castable riser: yes, I think that would be an excellent idea! Very heavy, but it would work great. Especially if you wrap it in that rock wool blanket stuff.

  14. Great show, I love when Paul comes on.

    Since my home came with two wood burning devices (Tarm wood furnace for hot air heat and water, as well as a small wood stove in the living room), I am always looking for ways to make them more “rockety” (my wife thought the bricks I put in the furnace to channel the flame and absorb heat might explode!)

    That being said, given that this rocket stove technology is so efficient, are there any commercial stoves or furnaces that use this tech? (the idea of a home built oil drum rocket mass heater stove in my living room might save me a ton of wood, but there’s this whole aesthetic thing I have to deal with.

    Thanks for the great show guys!