Unlocking Efficient Heat: A Deep Dive into Rocket Stoves and Mass Heaters with Matt Remine

In this episode of the Less House More Moola podcast, host Laura interviews Matt Remine, an expert in rocket stoves and rocket mass heaters. They discuss the principles behind rocket stoves, their efficiency compared to traditional wood stoves, and the importance of thermal mass in heating systems. Matt shares insights on building rocket mass heaters, particularly for small spaces, and offers resources for those interested in DIY projects. The conversation highlights the benefits of sustainable heating solutions and the practical applications of rocket stoves in modern living.

Matt's Links

https://walkerstoves.com/

https://www.youtube.com/@broaudio

Go to thetinyhouseadviser.com

Transcript

Less House More Moola Podcast (00:40)
Well, Matt Remine, welcome to Less House More Moola podcast. I am super excited to talk about this really great thing that you help people create and that is sort of an all purpose, works in small spaces, cooking, heating, even heating water stove. you and I connected.

for listeners benefit because I'm gonna build one here in the cabin in Colorado that listeners know that I'm over here working on all the time. So we are gonna talk about what a rocket stove is and about the stoves that you have created models for. So thanks so much for being here.

Matt (01:21)
Thank you so much, Laura. I'm excited to be here and I'm really excited to ⁓ hear more about your project as well as we look at it. You're in your cabin there, so it's really cool to see that. And thank you. Yeah, I'm excited.

Less House More Moola Podcast (01:33)
so talk to us a little bit about how you first came across the rocket stove and how you got introduced to this concept. I learned from permaculture design course and for whatever reason didn't put two and two together here in the cabin that we should do this until I came across.

something on a message board or a website about the plans that you had available. So talk to us about how you first came to Rocket Stoves.

Matt (02:03)
Yeah, you know, my introduction was similar, not quite as direct, but I think it did come through with permaculture channels as well. So ⁓ I've always been interested in ⁓ being more efficient in everything I do and trying to, you know, optimize systems. I really enjoy that aspect of things. And so permaculture grabbed my attention in that way, the systemic approach to ⁓ living and efficiency.

And in the early 2000s, I bought a ranch up in northwestern Washington, kind of right across from Victoria, BC. And I was looking for ways to sort of, maximize ⁓ my systems there and be more efficient. I was really interested in all aspects of the things that we now know of as permaculture, know, growing food and a self-sufficient life and all that stuff. so I found permaculture.

⁓ and sort of gravitated towards a lot of those things and somewhere along the way and I think it was actually just I remember who told me it was just a friend of mine ⁓ a great guy named Norm Nilsson. Norm if you ever hear this thanks so much but he told me have you ever heard of these rocket stoves and ⁓ and so I started to look into at the time I was heating my home with wood with a big old box stove that was a legacy from the old owners and it was a lot of work.

I mean, it was a lot of work. was, you know, cutting a lot of wood every year and trying to get it dry and that climate is really difficult. ⁓ yeah, so I was I was very interested and motivated. And so in those days, sort of the main information for rocket stoves was a book called ⁓ Rocket Mass Heaters, Super Efficient Wood Stoves and How to Build Them by Ianto Evans. And he's

not local to me, but he's a Pacific Northwestern or down in central-western Oregon. And ⁓ it was applicable to my situation since our climates were somewhat similar. And so I was kind of captivated by the whole thing. And I just started playing with him, you know, and his book really is a very much of a DIY and in the traditional.

sense in terms of when I talk about rocket mass heaters, I'm really talking about, when I say traditional, mean just like the mud stove, know, just made out of cob and ⁓ built using the minimal inputs, know, financial inputs as possible, salvaging everything. ⁓ And that really appealed to me. And so I really did a lot of ⁓ experimentation and research. And yeah, so that was sort of my introduction was ⁓ a friend told me about them and then I found Yanto's book.

And at that time there was a little bit of online chatter about him, but mostly it was sort of ⁓ really stemming from Yanto's book and everything online was really a lot of kind of just reinforcing the things in that book. And I still think that that book is a great resource for people just coming to Rocket Mask Heaters. We've come a long way, but it actually does a really good job of laying out the foundation principles that I think a lot of us still...

hold to, know, there's still a big DIY component to the whole thing. And yeah, so that's how I sort of came into it originally.

Less House More Moola Podcast (05:27)
That's awesome. So talk to us about those principles a little bit. What is a rocket stove? What is the functionality and why when you had a wood stove is a rocket stove a superior option in those conditions that you're talking about?

Matt (05:44)
Yeah, so you know, this really goes back to the man who really, I'll say invented, ⁓ definitely identified the key principles and laid them out. And his name is Larry Winiarski, and he was an actual rocket scientist. And I think he worked for, well, I can't remember, Northrop Grumman, one of those big military conglomerates. And he's again a Northwesterner.

And he, I'm gonna get some of this wrong because I'm just kind of riffing off my memory here. But at some point he left his work in the military industrial complex and started working towards humanitarian efforts. And he was a part of Aprovecho

which is a organization out of Portland they really focus on humanitarian efforts and finding ways to help people provide for themselves in more sustainable ways and really with a focus on, like I said, humanitarian. So like when there's, famine or crises in all parts of the world, they'll send their technicians, people who have researched ways to...

cook food very efficiently or, provide things that people need in ways that are much better for their environment and that they're capable of doing regardless of their economic situation. So Larry Winniarski started working with them and what he did was he really boiled down what a rocket stove is. And now we're kind of bouncing between two different words, rocket stove and rocket mass heater. So a rocket stove,

is the combustion core, the front end, the way that the wood is burned. And then we use those in a rocket mass heater. We use that rocket combustion core to heat our thermal mass. So we're kind of talking about two separate things that form a system when we talk about a rocket mass heater. But the rocket stove is really the foundation of it. And Larry's principles were very simple. And I have a video on my YouTube channel, which is https://www.youtube.com/@broaudio All one word, B-R-O-A-U-D-I-O. I thought I was going to...

make videos about ⁓ music stuff, but I didn't. So that's why they have the funny name. ⁓ But I have a video on there called the 10 Principles of Rocket Stoves. And that is directly from a paper by Larry Winiarski. ⁓ And it breaks down all 10 principles. I won't go over all 10 of them here because some them are with regards to measurements and stuff. But really, this is going back to your answer about what makes it better than a box stove. And, you know, we burned

wood forever. And we typically approach it in a certain manner, which is just like light it on fire and try and get the heat out of it onto us. Sort of, that's it. And Larry really identified that that was really inefficient because what you're doing is if you pull the heat right from the fire, you cool the fire, you know, obviously you're taking some heat.

and you really reduce its ability to consume all of its fuel completely and efficiently. And so his principle, really what a rocket stove, the most basic way I can describe the principle, is that it's a way to consume the fuel completely and then extract the heat for us. what we do is we, some of the principles are mainly insulation and reflection back onto the fire and not removing heat until after combustion is complete.

And in that way we can have a much more efficient fire and we can then extract the heat afterwards and we can get a complete burn, which means a lot less smoke and un-burnt fuel and things like that. And so again, to tie that back into your question, a box stove really functions on the first purpose, the first ways that we burn. You light the fire and it heats the metal and the metal heats us and that's great, but what's happening is that, you know, the...

as that fire burns, it's just creating heat that's going straight up. And as it's going straight up, it goes out the chimney and it accelerates things because of the draft. And so now it's drawing air in and burning it quickly and blowing it out. And because of that, it never really has time to burn completely. You know, the gases escape the hot zone very quickly. And so I could go on and on. Obviously, this is something that I love, the technical side of it, but to keep it fairly simple,

That, at the simplest level, that's really why a rocket stove is so much more efficient. I want to say better, but ⁓ I think it's better, but more efficient than a box stove or an open fire or a fireplace. Because when those type of combustion events happen, the combustion just happens right at the wood. And the wood isn't the fuel. You're just heating the wood. And then that's creating wood gas.

and it's the wood gas and the oxygen combined that are the fuel. And when they are just allowed to escape as quickly as they're being created, well, you're just burning a very small percentage of that wood gas and oxygen that you're actually feeding into that combustion area. And so it's very inefficient. And a rocket stove is designed to focus the heat of combustion back onto those fuels and to sort of slow down, slow things down and

stall the fuels in the hot zone and create a much hotter hot zone and a longer hot zone so that you have a chance anyways of completely combusting the fuel before it escapes. So ⁓ in that sense, know to me that made a ton of sense in what I first looked at it and I knew because I was cutting down trees and chopping wood and stacking wood and trying to dry wood, you know, I knew how much work

it was to heat myself with wood in that box stove and I thought to myself, wow, if I can go from 30 or 40 % efficient to 80 or 90 % efficient, that's a whole lot less work that I have to do and I'll have that much more time I can put into fixing the fences or planting the garden or whatever it might be. So...

That's really the big difference and that's why I, you know, what I identified as appealing ⁓ to me about a rocket stove and a rocket mass heater.

Less House More Moola Podcast (12:12)
That's fascinating and super nerdy because I don't think most people are aware of that. You know, burning wood is quite inefficient or that you're actually burning the wood. You're burning the wood gases and the oxygen. That's really quite interesting. I came to this, you know, concept. I fun fact, I grew up in a, in a basement and two story house in Virginia in the woods where we heated our entire house with a wood burning

furnace in the basement. And so we cut wood and cut wood and cut wood like that was our hobby and our vacation and our weekends in the snow in the spring in the fall like that is what we did is we cut wood and stacked wood and hauled wood all the time. And so when I went into my adult life like I was really glad for that to have passed and then like many things in childhood we come back to them and we find some sort

of strange adult pleasure in the things that we did when we were a child and now I'm like let's go cut wood but in this cabin we had a propane furnace that was here when we got here and we've used that over the past winter and then I started looking for antique wood stoves for the cooking part and so I'm like doing this search for antique cooking wood stove because I guess I think I'm going to

to

if we think about it from a resilience or a self-sufficiency standpoint, that's something maybe that is.

more likely that we can always source for ourselves or what have you. And so it was from that antique stove that I realized, hey, same thing's happening here. We're heating up this stove and it's like cooling off super fast. And here in Colorado, we have, you know, cold winters. I need some more thermal mass. And so we're working on a Adobe greenhouse for thermal mass. But then when we're going to use our heating, I want our heating to create thermal mass. I'm like, ⁓ duh, rocket stove, right? And so we're back to that.

And so let's talk about the thermal mass part of this and how that can just be such a game changer in terms of that constant feeding the fire.

Matt (14:30)
Yeah, so actually, while we talk about that, I'd to go back to the box stove just a little bit because it ties into that. you you're talking about how your box or your cook stove ⁓ you would like to fire and it's blazing hot, like crazy hot, and then it's cold and it's out. And, you know, in typical box stoves, that's what happens if you run them open. And so, of course, what we've adapted as our standard with box stoves is we crank them down, we close the air off and we

starve the fire and we smolder the stove, you know, and I did this forever before I got wised up, you know, I would try and make the fire burn all night, you know, that was like your goal when you have a box stove. And all you're doing, you know, is now you're burning at like so low efficiency because it's just, you know, simmering away in there and there's no heat to re-burn those gases. So, you know, that's when you're making a ton of smoke out your chimney and that's when you get a...

dangers with chimneys because you get the creosote stuck on to the recommendations. They're like, burn it hot for a while and burn that stuff off and then try and make it through the night and smolder it again. And ⁓ you know now coming back from the rocket stove world, I look back on that and go, geez, that doesn't make any sense. But to so many of us, that's normal and that's the right way to do it. And so with a rocket mass heater, one of the reasons why it's so efficient is because it only burns

at full tilt. just goes flat out as hot as you can get it and because of that the burn cycle is very short in a standard rocket stove which has what we call a J tube combustion chamber and we don't need to go too far in the technical details but it doesn't have a door and it doesn't have air settings. You can't close it off and you can't smolder it. And so because of that the burn cycle is very short in duration.

And so you need a way to capture, you know, if you're going to get any kind of long usable heat cycle, you need a way to capture that heat. And we talked early on, we first started about how with a rocket stove, you know, the, ⁓ the goal of the function is to burn it hot and completely, and then capture the heat after the combustion stage. Whereas in a box stove, it's all the same thing. It's the combustion stage and you're trying to get the heat out of it right there. So with a,

rocket mass heater, what a rocket mass heater is, as I said it's a rocket stove and a rocket mass heater, a rocket mass heater is a rocket stove, Larry Winiarski's super fast burning, super hot, super efficient combustion unit paired with a thermal mass storage capacity, we'll call it a thermal battery if you will. And so very important that you have

that element if you want to get sort of a longer heat cycle. And, you know, a lot of people ask me, well, why can't you just do that then with your box stove? And the reason is, is because there's no way for the box stove to burn extremely cleanly. You won't be able to combust all of that fuel. Now, fuel, as I said before, is the wood gas and the oxygen. If you don't combust it all and then you cool it off inside of something, you'll get a ton of creosote.

and you'll create a dangerous situation where later on that creosote could reignite and cause a chimney fire. And so that's why box stoves have really hot, you know, the chimneys are hot and they're usually insulated to keep the heat in. And that's how you blow all that unburnt fuel out the roof in the form of smoke and particulate and stuff like that. But so it's not dangerous in your chimney. So to answer your question about long heat cycles and thermal mass, with a rocket mass heater, we combine that super efficient front end

And then we take that exhaust gas, but it's very clean because we've burned it completely. We've been, you know, completely combusted the wood gas. And so we can now put it into a thermal mass. And that thermal mass is something that captures the heat so that it can be released slowly over time into the space later. Now in doing that, you're going to cool off the gases. And like I said, it's okay to do that now because we've gotten the creosote, the wood gas out of there.

So what we do is we burn that rocket stove and then we channel the gases, the exhaust gases, through some form of thermal mass, some way, something that captures, some material that captures heat and gives it off slowly before we then exhaust it out of the chimney. And that does a couple things. By capturing all that heat in our thermal mass, we then have very cool exhaust. And that means we can deal with that exhaust in...

much easier ways than trying to run a 700 degree chimney pipe through your wooden structure. So you get a much safer ⁓ chimney, in my opinion. You also don't get the danger of trapped fuel creosote stuck there. And now to go back to your exact question, is the rocket mass heater, what is the mass? So the mass can actually be any number of things. What we want is we want something that we can heat up with those hot gases and that will

hold the heat and then release it into our space over time. the very... there's ⁓ different measurements that we can use to evaluate materials that you can use for thermal storage. know, density is really important. Something that's really dense will be able to hold a lot of heat and it will give it off slowly. There's also a term called emissivity and that is

actually ⁓ a property of a surface and it's how it radiates heat and things that are the highest emissivity are black. They're usually flat like a matte black and those will radiate heat as radiation ⁓ very well. Things that aren't very emissive, don't have a high emissivity are things that are shiny like a shiny stainless steel. It just kind of reflects the heat back into itself.

and it won't send it out. And so what we want for thermal maps, we want something like I said, that's dense and hopefully sort of dark and matte finished on the outside. And so a rocket mass heater takes those clean gases and we run it through something. Now, I talked about Ianto Evans, the original rocket mass heater sort of, you almost say inventor, but ⁓ he gave us all this knowledge and innovator, I guess would be a great word for him. ⁓

And his method, like I said, he was really focused on DIY, his method was to run standard chimney flue pipe through a large mass of cob, which is a mixture of clay and sand, usually with some straw and it's all together. But it's basically what you would make adobes out of, you know, like a mud clay brick. Any kind of mud clay building is the same sort of material. And so the original rocket mass heaters had the flue pipe running through a large mass.

of this mud and clay we call it cob and often built into like a bench to sit on or sometimes ⁓ a big, you know, sort of monolithic tower structure to radiate heat back into the room. And this is very similar and it's all the same theories that we see in European masonry heaters. And I would say that, you know, they're all in the same family. They're all masonry heaters, masonry being something built out of, you know, stone and sand and clay. ⁓

And in Europe they would use ⁓ tile or tile covered bricks ⁓ as the mass, thermal mass. So, and again, that's really just kind of fired cob. It's sort of just a more refined version of Yanto's DIY version. ⁓ So there's a couple versions of Rocket Mass Heater, a cob as the thermal mass, a bench that you can sit on. One thing that's really nice is ⁓

using conductivity to put the heat into the humans in the room, which is why a bench is nice, because a human can sit on the bench and get that heat through the conductivity with this touch of skin to the masonry. ⁓ They will radiate into the room like a box stove does, but not quite at the same rate. They have lower service temperatures, obviously, than a box stove. so, conductivity is nice. So it's nice to have a place where you can sit or be close to.

this cozy masonry mass. one more thing I should touch on as we're talking about thermal mass and rocket mass heaters is the mass can also be things like water. And water is actually the ultimate. That isn't to say I prefer it and it's not always the best because it comes with a lot of compromises. But when I say ultimate, mean just by the numbers. ⁓ Water can store a lot of heat, a lot of heat, and it can give off that heat.

over a very long period of time. You know, we all know how much energy it takes to go through like phase change with water with returning from boiling water to steam. It holds at 212 degrees because of all the energy that is being utilized. And we don't go through the phase change in a rocket mass heater, but that's just an example of how efficient it is at storing energy. can take a lot of energy. It's a great energy sponge. ⁓ You all know from heating water, takes a lot of

energy. You might not see it in your electric bill or your propane bill. It takes a lot of energy to heat water, but on the flip side it stays hot for a long time. And so ⁓ when we talk about a rocket mass heater, there's a lot of shapes and variables. There's a lot of different types that there can be. ⁓ And just to wrap that up, the classic one is sort of like a DIY. This comes again from Ianto Evans. Sort of what he put into all this is that, this is a cool way that you can heat your home.

with something you can build for not much money. so those ones you typically will see a rocket mass heater as like a cob structure that people have built using very little financial input. But like I said, it also can encompass things like a beautiful masonry heater that is the centerpiece of a multimillion dollar home. you know, those things could have cost hundreds of thousands of dollars just for the masonry structure at the heart of the home. So there's a really broad range.

⁓ But that's sort of the gist of a rocket mass heater and that's the mass component is really what's important. It allows us to have that hot, efficient, clean combustion unit and still have a reasonable heat cycle. Like I said, at the very beginning the stove only burns for 30 minutes or an hour but if we combine it with thermal mass we can now get eight hours of heating out of that one hour of burning or something like that.

Less House More Moola Podcast (26:32)
Yeah, I think that's the key takeaway there is, you know, short burning time, long heating time, and that's the huge benefit as opposed to having to feed the fire, feed the fire, feed the fire all the time. I do want to come back to how you have, you know, over your years of experience sort of honed in on what you feel like are good build components. But I want to go back to the clean burn a little bit because those of us in tiny living obviously are focused on our footprint.

often and the way that we're impacting the earth and I noticed on your website some of the EPA ratings or certifications or what have you that you have listed there and one of the things that I have encountered recently is we bought ⁓ you know off the showroom floor wood stove for our tiny house that everyone who's ever seen pictures of our tiny house will have seen it in there we have never effectively burned a fire in the wood stove because it's a post

Matt (27:30)
you

Less House More Moola Podcast (27:31)
2015 wood stove, which I guess the EPA instituted some of that maybe efficiency of reburning of the fuels, but it has prevented us from ever having a successful fire in there. And this is a whole like rant I could go on about how challenging it has been, especially for a girl that grew up heating her entire life with wood. And I've been building fires my entire life to have this wood stove be so difficult to deal with. And so I want to talk

about how kind of like maybe you have some insight and how that kind of played out with regular wood stoves and how a rocket stove ⁓ works differently but still produces the same result from an EPA and cleanliness perspective.

Matt (28:20)
Yeah, we could do this for hours. I could go off on that subject forever. So just a little background, in 2013, ⁓ there was an event put on by the Department of Energy and MIT, ⁓ USDA, a whole bunch of entities came together and they did something called the Decathlon for Green Heat. And it was held on the National Mall in Washington, DC.

Less House More Moola Podcast (28:22)
I'm

Matt (28:50)
and they took entries from all over the world and they chose finalists and I saw it in Popular Mechanics, I think, on their website, I guess, and I entered and I was chosen as one of 13 finalists. And the other finalists, there was one other person like me, a wonderful man from New Zealand, but all the other ones were Lopi Woodstoves and ⁓ Hearthstone Woodstoves, know, big, big manufacturers

I mean, I ran into the founder of one of them and he was like, I've sold, can't remember what the number, it's been a long time, over 10 years now. But it was like a billion dollars worth of wood stoves over the last 20 years. I mean, this was industry that I was hobnobbing with. And the people there who were testing and all that were the EPA and were the USDA. And we got to talk about the regulations and the measurement.

practices and all of that stuff. So I got a real look at what you're talking about. And honestly, that moment, that week that I spent out there ⁓ was very formative in the way I run this very small business now in selling plans because I sort of knew that I would probably never be able to sell a physical product. At the time, I thought I was sort of going down the road of building a product to sell.

But because of the regulatory environment, I realized that probably wasn't gonna be possible and I won't go too far into it. But to make a long story short, the regulatory environment was built around testing box stoves. And as we talked about earlier, a box stove is designed to smolder for eight hours so it can burn overnight. So the test takes like four hours. Well, my rocket mass heater was done burning in like 35 minutes or something.

So it doesn't even fit into the test format. They haven't finished their warm up phase of their test. So my first goal to even be able to bring something to market to get an EPA stamp on it would have been to change the entire bureaucracy of how they test stoves. And they've been working on it ever since and it still hasn't changed. So now to go back to your prompt about wood stoves and modern wood stoves, ⁓ again, you know, because of

our acculturation, I'll call it, you our long history. Ben Franklin created the Franklin stove back in whenever it was, I'll get the year wrong, but let's say 17 something. it was when they kind of went from open fireplaces to metal stoves. And in all those hundreds of years, you know, the normal way of burning was to

smolder your stove so you can burn it for eight hours. ⁓

As we've become more focused on efficiency and with pollution policies of the 70s and 80s starting to come into play and people started to look for cleaner solutions because that's a terrible thing to do. just smokes out your chimney and wrecks your whole neighborhood and there's particulate everywhere. Everyone's breathing. It's really no good. smoldering a wood burning stove. And so we started to look for ways to make them cleaner. no one was willing to have a

burn for three hours. The real answer is just burn it really hot and it's clean, but then it burns for an hour and then you're cold as you found out with your very initial prompt in the very beginning of the show. So what they started to do was find ways to try to get cleaner burns while smoldering. And so these modern stoves like yours, I assume, use two methods. Usually one is catalytic and that's a way that we pass the gases through various

elements like platinum, you know, it's just like a catalytic converter in your car. It's the thing that everyone gets stolen because it has valuable elements inside, heavy metals and things like that. And what happens is that it's called a catalytic converter because those heavy metals are catalysts for burning. And so where I was talking earlier about focusing heat back on combustion so that the volatile fuels burn off completely, well those volatile fuels burn off at high temperatures.

1100, 1200, 1300, 1400 degrees Fahrenheit. If you pass them through catalytic elements like platinum and other heavy metals, you can lower the temperature at which they burn, right? Those catalytic elements give off one of their molecules and you lower the combustion. Now you have a different fuel makeup and it combusts at lower temperature. So these are efforts to get stoves to burn.

cleanly at lower temperatures so we can smolder them. So there's catalytic stoves and then the other one is secondary air stoves. And again, it's the same thing. You starve the stove of fuel in the front so the wood smolders and makes wood gas and then they try to inject more oxygen into a hot phase later on to then get a proper fuel air mixture. Wood stoves are just like carburetors. If any car freaks are out there, you know, it's really just all about fuel and air.

And so the secondary air stoves where they put the air in later and try and do that in a hot place. And again, it's an effort to try and burn off these volatile chemicals in the exhaust. ⁓ But what that means for you as the stove owner is really a very finicky burn, like a really narrow burn profile. You know, the stove has to be

just hot enough to re-burn the stuff, but not so hot that you're warping everything, because now they're kind of fragile in the back end, as we'll say. they, you know, like you can, secondary air stoves, if you just run them hot, you know, wide open in the front end, you'll just melt the secondary air stuff. And the same with the catalytic stoves. They have a catalytic element in the back. And this isn't to bash on them. There's actually amazing technology. And I, you know, I won't do it now, but I can give you some great recommendations for...

There are modern box stoves that are pretty darn good actually. ⁓ most of the best ones are hybrid and that's a combination of those two things, catalytic and secondary air. But again, they still have really narrow parameters and the fuel has to be the right moisture content. You have to have the air settings just so ⁓ depending on what fuel species you're using and...

you know what your outside air temps are because of your draft is pulling air at different velocities, you know, like you need it to go just right through the critical section. It's very finicky and not only is it very finicky, but those things, the catalysts and the secondary parts, those are all wear parts and they need to be replaced regularly. And if you're not within the narrow operating range, then the maintenance schedule goes way up. You plug the catalyst with

Creosote or you burn it too hot and you melt it all down too early. So yeah, it's a nightmare kind of in a lot of ways and And that's really another one of the things that drew me towards rocket mass heaters You know when I moved into my house my ranch house originally it had like a homemade big metal box stove and It was super inefficient. It just chewed through wood crazy hot chimney fires like

on the regular, you'd have a chimney fire on purpose every week so you didn't have a big one every month or whatever. ⁓ And I was really seeking a solution just like you guys were when you bought your box stove. And so I went box stove shopping just like you guys did. And I never got there because I ran into Rocket Mass Heaters first. And you can hear the way my mind works. I love systems. And I instantly identified, I was like...

that makes so much more sense to me. Like, why don't we just burn the stuff really hot in a way that's safe, that we're not blowing the super hot stuff out the chimney, and then we'll capture the heat later and we'll store it we'll have super short, hot, very clean fires. So I don't remember if you had a question about the box stove, but that kind of really sums it up. ⁓ and maybe tying back into the regulations. I think I touched on that too, you So really a rocket mass heater, it burns.

It's as simple as its burn cycle. It's sort of outside the way those box stoves are designed to burn. And so with regards to EPA and certification, it's really all just a function of the way they're tested. But if you actually look at the numbers, the rocket mass heater burns. I'm not one. I am one for hyperbole, but in this case, I'd like to be pretty realistic. And I won't say there are some great box stoves out there.

But a rocket mass heater is as good as the best of them and a lot of people say better than any of them and I think it's possible for it to be better than any of them but nonetheless, you know, it's easy for a rocket mass heater to burn at 80 % efficiency. That's extremely difficult for a box stove. Rocket mass heater burns at 80 % efficiency. It also has a big stratification chamber or a place where the gas is slow so particulate can percolate out, precipitate out, and so they're very clean with regards to particulate.

There's just, they make so much sense and they, in the way, you know, in the ways that we want them to be clean and the ways that we want them to be efficient, they just are by nature of the way that they are built. And it's obvious once you sort of get under the hood, you're like, ⁓ I can't really have a chimney fire. There's no creasote and there's no super hot gases going there. the particulate precipitates out through all this mass that it flows through.

So we're going to blow a lot less PM 2.5 out the chimney. We don't need to be so concerned about, you know, these things. we don't have catalysts and we don't have second, I mean, some have secondary air, but you know, we don't have the same fragile kind of systems. Yeah. I don't know if that answered your question, but that's, you know, they make a lot of sense when you kind of look at them and the box stoves require a lot of, ⁓ I don't know how to say it.

They don't make much sense. Unless you really, you know, yeah.

Less House More Moola Podcast (39:18)
Yes.

Yeah, I feel like that they were like an, they were engineered, right? For a particular goal, but not practical for, you know, the everyday person who's just trying to, hey, we've got a cold light, let's keep the woodstone tonight.

Matt (39:25)
Yes.

Well, yeah, like

I said, it's, mean, they're basically still Benjamin Franklin's Franklin stove technology. It's a metal box and you light a fire in it. And wow, that's really nice and warm, but it only burned for 45 minutes. I want to load it up and have it still burn and be burning in the morning. So I'll just shut the air down. We're still there, you know, 100, 200 years later, 300 years later. That's about as much sense as they make.

Less House More Moola Podcast (39:59)
Yeah, I wish mine was catalytic because then I could put it out in the Walmart parking lot and maybe someone would, you know, steal the steal the precious metals out of it and find some value. I think it's probably that secondary air type that you were talking about. And ultimately what happened is that we never could use it because the minute that we closed the door, it killed the fire. And then the smoke emanated out of the door and in the seams of the pipe and completely smoked out the entire tiny house. I have on numerous

Matt (40:05)
Hahaha

Less House More Moola Podcast (40:29)
occasions taking cooking tongs to take the wood pieces out of the stove and throw them out the door because we never get and we've tried multiple times and we read all the things and we you know like I know you can modify whatever anyway completely useless paper weight and I see a lot of the exact same stove on Facebook marketplace and so I'm super excited to move on from that but let's go to the build piece of it and how you have ultimately

we refine and optimize what you view as a really good, you know, rocket mass heater build process. We're going to build one here in the log cabin. And if I wasn't excited about it before, which I was, I'm like super excited about it now because we're in a wooden structure, right? And so having fires is of significant concern. We are going to have to reinforce our flooring, our floor here, our floor system before we can start building it because it's very,

heavy and I've been looking for bricks on the Facebook Marketplace and things but talk to us about kind of the basics of the build process that you have refined.

Matt (41:39)
Yeah, I'd love to. you know, I talked a lot already about Ianto Evans and his original sort of, ⁓ it was a rocket stove that ⁓ exhausted into a 55 gallon drum and that 55 gallon drum provided like a nice quick radiant heat like a box stove kind of does. And then it would, he would route the gases into a cob thermal mass. And I built that way for many years. ⁓ You know, but people were always asking for something that was aesthetically.

more pleasing. There's a lot of different tastes out there and different spaces where they go and so not everyone wanted an oil drum and not everyone wanted a cob sort of round blob of mass in there. And I also did a bunch of workshops where I was sort of on the go and bringing materials with me and sometimes taking them down and then bringing them somewhere else to rebuild. And I would also get a lot of people question...

asking about masonry heaters, which we touched on as well, which are often, you know, really large center of the home centerpieces, but they're often built ⁓ just with bricks and then usually skinned with like soapstone or other high-end things. Masonry heaters are, the classic sense, European sense, they're wonderful and our rocket mass heaters are masonry heaters, but the difference really is just in those materials and the cost. know, a rocket mass heater originated as a DIY thing that you could build for very low cost. A masonry heater was

always the realm pretty much of rich people because it really required usually a very skilled mason to build it and the typical ones you see in this country are like soapstone covered giant structures and I'm not exaggerating, they're 70, 100,000 dollars. mean there's cheaper ones but even cheap ones are 20 or 30 thousand dollars for like a Tula Kiwi from Finland kit or something like that which are wonderful and beautiful and I'm not...

⁓ disrespecting them at all. But with all these people coming to me and saying, you know, we're somewhere in the middle, we want to be a DIY build, but we don't want a mud pile in our living room. What can we do? And I really started gravitating towards the idea of a masonry heater type build. And in that sense, you know, I identified that bricks, just a standard red clay brick, are a wonderful way to build a rocket mass heater or any sort of masonry stove. You know, they're

They're inexpensive, they're really ⁓ available everywhere. One thing about them, they're not consistent. ⁓ they're different sizes all over the world and even all over the country. ⁓ So that's really something that's interesting because what I always recommend people do is just play with them like Legos. And that's one of the most appealing parts about them for me. You people get real apprehensive when they haven't worked with them before and they're like, I don't know anything about them. say, you do. It's just...

building blocks. You did it when you were two and once you put some in your hand and just play with them and this is always what I recommend, everyone's first step and I'll recommend it to you guys too. When you find some bricks, spend some time just playing with them outside, just stacking them up and seeing, that's how that might go together. ⁓ we could do it like this. And instantly, know, your light bulbs will go off and you'll answer so many of your own questions. And so to answer your question for materials, I started gravitating towards these brick builds and ⁓ you know, I

To me, they just make a lot of sense. I've really come to, I've settled on that. And it's not the only way I'll still build with cob if someone wants to. you know, like if we have clay and sand in their yard and it's free and everyone wants to do the work, it's fun. You know, I really enjoy that. But the bricks make a lot of sense. You can often salvage them. If you can't salvage them, they're really affordable, even at places like Home Depot. ⁓ I think prices have gone up since I last priced it, but you can still probably buy enough bricks for 300 bucks or something like that.

to build a pretty nice stove. ⁓ like I said, they're just building blocks. They're really dense compared to the Cobb since they're fire. They pack more mass in the same volume. So they're very efficient in that sense. You can have a smaller stove that has the same thermal mass. So we'll have a similar long heat cycle. And to my eye, they're aesthetically pleasing. And if they're not, they're a wonderful inner structure. So then you can do the outer.

aesthetics the way you like and then if you have the budget you can cover it with soapstone or if you prefer the plaster cob look you can skin over it with Plaster or cob you can do whitewash ⁓ You can do tile, you know, there's a million Maybe not a million, but there's a lot of ways you can cover them ⁓ To match your aesthetic and so they're very flexible in that regard They're affordable and available and they just work great and they're and they're really fun to build with so for me ⁓

You know, and actually it does hearken back to, we have a long history of masonry heaters in European culture for sure. I say we, but you know, really just humans is what I mean. Going back to ⁓ thousands of years actually, like Kang stoves in ⁓ Korea and in China and Japan, they had similar underfloor heating. And even the Romans, ⁓ the Romans had the underfloor heating ⁓ in their baths. And those were basically masonry heaters. They were built underneath.

tile floors with their Roman mosaics. So we have thousands of years of history of building in this manner. ⁓ And so yeah, it just makes a ton of sense. And I definitely have ⁓ latched onto it for my builds.

Less House More Moola Podcast (47:17)
I think it's a good balance, right? Because I, you know, I love the idea of cob too, but maybe not in my kitchen. And everybody has for their whole life been exposed to a brick fireplace. And so that, you know, it just feels comfortable and normal for us to have, you know, brick on the interior. ⁓ I saw the original type of rocket mass heater ⁓ in an Airbnb where it was a permaculture, you know, project out in

⁓ Cortez, Colorado. And that was like at the time I didn't know what it, you know, didn't really know what it was. And then that kind of like came back into my mind. But yeah, like having that 50 gallon drum in your, in your space, maybe it works in a barn dominium. Maybe it doesn't work in a, in a nicer space. So for the tiny home, you know, focus listeners, you actually have really small plans available for really small spaces.

And also you have plans for larger spaces. You want to talk a little bit about what all plans you have available.

Matt (48:23)
Yeah, sure. know, I just like to actually, it's not a correction really, but the rocket mass heaters, at least all the ones that I designed, are designed around basically a chimney size. So, and we always kind of just try and use six inch chimney, has the standard chimney. And like I talked about earlier, they're kind of like carburetors. The chimney dictates how much air you're going to be able to move through this thing. And so with regards to power,

the chimney size really dictates the power. And so with six inch chimneys being the norm, and it's actually really difficult to get much smaller than that, I became interested in trying to build the smallest heater I could because I've always lived in tiny spaces, not always, but for the last 10 years or so I've been in very small spaces. My last cabin was about 15 by...

17 on the longer side, like 13 and 14 and 17 was sort of an odd shape. ⁓ you know, I came up with what I call the tiny cook stove, which is a very small rocket mass heater made of bricks with a cooktop and an oven in an effort to try and provide all of the function that I needed in one stove, but it still used a six inch chimney because like I said, as soon as you deviate from the six inch chimney, you get into a whole host of...

other problems with regards to just material. inch jimmy is the normal for construction so it's much easier to use. And also just ⁓ your firebox just gets so small if you go below that because all the sizing inside the combustion chamber is really dictated by how much air can be drawn up and when you limit that air to a 4 inch jimmy or the next size down from 6 inch everything just gets kind of too small and now you're cutting really small wood and now you're really having a hard time.

getting any meaningful heat out of it. So my interest was in building the smallest sort of reasonable rocket mass heater that I could. And so ⁓ that's the tiny cook stove. And like I said, it was designed around my interest in living at small spaces. Rocket mass heaters make a ton of sense, especially the all brick ones like I like in small spaces, because you can have much closer clearances than you could with a box stove. And they're also much more comfortable to sit on and next to and with.

You know, where it's a box stove, people only just think about the space that you need behind it, but the reality is, is there's a huge dead space, a big bubble all around it, right? And if you live with one, you know, you know, your hearth is big and you don't put stuff too close and you gotta watch out for spars coming out of the front. And so they really, you know, they take up a lot of room. And so the tiny cook stove was my effort to make it as small as possible. And then from there, really, you're just expanding.

the body of the stove. And so I have other plans available. Larger cook stoves then incorporate larger ovens. And I have larger mass heaters that have benches and taller towers and things like that. But to go back to the beginning of what I started here is they're really all the same combustion chamber. And the outsides are really, this is a really important point for anyone interested in these things. The outsides are highly modifiable.

We suggest you don't modify the core at all because it's carefully designed to burn completely and completely efficiently. But after that, the brick, it's just really a series of brick boxes. And they are incredibly malleable to fit your space. And so I sell many different plans with different sizes and lamps. But I like to think of them all as starting points. And I really encourage everyone to, like we've talked about, get some bricks.

dry stack you know take a look at the plans and know what your goals are what the internal paths ways are going to look like but from there you can take my rectangle and turn it into an octagon because it fits your dining area or you know stretch the bench out over here or squish everything this way and make it taller because that's better for your footprint and so that's one of the beauties of the stoves and the way of building and I do offer ⁓

I don't know how many, quite a few different shapes and sizes, but essentially they're all just variations on the same basic stuff.

Less House More Moola Podcast (52:51)
And you offer consults for folks that need little bit of personalized guidance.

Matt (52:56)
do, yes, you can purchase a consultation off my site and ⁓ we can chat. And for anyone who purchases plans, I'm always here for you. The email, I spend a lot of time answering emails every day. And I love to do it. I love talking about stones. can tell I'm passionate about it. And I like seeing what people come up with and helping them find solutions. It's fun problem solving. And so any purchase of plans, you've got me on your team forever via email. If you want to

get face to face. do offer consultation and those can be very helpful for people who usually it's for someone who has a pretty good idea of what they want to do but aren't quite sure how to achieve it. ⁓ I also on my YouTube channel I have just a ton of information about sort of the basic questions one might have on their way to finding out about these things and whether they might work for them and so I tried to make it a searchable database ⁓ in the sense that I...

pared down a bunch of presentations I did and titled them with appropriate titles so you can search what kind of material do I want to use, should I use bricks or should cob. You can do a lot of searches on my YouTube, Bro Audio, and hopefully find a lot of answers to help you least get started on building. And even if you don't want to buy my plans, I love emailing about stoves, so ask me questions if you want to. I love to talk stoves.

Less House More Moola Podcast (54:21)
we've got links for you, walkerstoves.com and YouTube at BRO, A-U-D-I-O at BRO Audio. making sure that those are in the show notes for everyone. Matt, thank you so much for this really great conversation. I think, in my learning about, rocket stoves and rocket mess heaters, now which I understand to be two different things, I didn't really fully understand

kind of the nerdy bits behind the scenes and why they are so beneficial and can be such a superior way, not only for our heating purposes and practical use, but also for particulates and cool exhaust and you know, just all those things and your insights having been in the thick of like the box stove world when they're trying to make it more efficient is just tremendously valuable. So thanks

much for sharing all of those details.

Matt (55:23)
Thank so much for having me. It's been a lot of fun. I love talking about it. It's been a real pleasure. Thank you.