Joshua Myrvaagnes

Thanks, this gives me some good information.

The bucket of water on top is propped up on bricks around its circumference, mimicking the Cob hat, i’m not sure if I had mentioned that.

I’m going to thicken the Cob that surrounds the second barrel for sure, cob higher on the first barrel, and also ask the person who helped build it how much space was between the riser and the barrel. I think it may have been more than 3 inches, and I think it would actually be worth it to concentrate the heat more in the center of that barrel, so that it would be really directed at the tub of water to be heated rather than radiating into the room.

Another issue is that the Cob hat is way up in the air—not where people are. I put a metal bonnet on top of that to reflect heat down again, but it’s not very ideal.  It doesn’t feel like it’s radiating a lot of heat when the fire is out, but I suppose that that’s not so easy to feel unless you’re right up near it.

The burn tunnel is 33 inches long, I believe, one extra length of brick. I’m understanding you’re saying that that is a serious problem, yes? Do you know why that creates more ash instead of Heat?  

One obstacle to changing that is that the size of the barrel is 65 gallon rather than 55, and there’s not very much space between the firebox edge, and the edge of that barrel currently. Almost none. Certainly not 9 inches. And I thought we had solved the problem of the extra burn tunnel by making the riser taller…?

Another thing I’ve discovered is that I can cook or reheat a pot on top of the firebox, as long as I don’t let it boil over, the firebox radiates a lot of heat upward. Even though the draw down is very powerful.  My pot got up to a boil, reheating some starch.  This is helpful because I have sacrificed to the top of the barrel to just heat that big tub of water.  My friend still has a way to make a pot of buckwheat for dinner without needing to use electricity.

Another factor I just realized I should mention, this is the sunroom, it gets really good Solar gain in the daytime, but has terrible shades at night. Some of them are r2 beehive, shades, and some are just a thin rough-weave cloth, which hopefully traps a little bit of air between the glass and the curtain.

Yesterday, when it was about zero Fahrenheit outside, which is not the coldest it ever gets here, it felt like the cold was reaching fingers into the room. I was sitting right next to the rocket mask heater after the fire had gone out, and I was wearing my coat. I made another fire and then I felt better.

At sometimes when I have measured the temperature of the chimney as it’s exhausting, it has been about 160°. I’m wondering if all the Heat is getting radiated into the room from the barrel, and it would actually be good to put Cob up higher around the bottom of the barrel?

Please forgive the weird capitalization of words, I am using dictate to type this. Thanks so much for your help.

Thanks for your reply, Glenn, I wrote back and I messed up the thing to indicate that I was quoting your post. I put my answers with a DASH (—) before it.

Joshua Myrvaagnes wrote:Some information we need to assess the situation would be the size and character of the house, its age, insulation, weathertightness, a description of the chimney...

What exactly do you mean by a baffle?


—I put a piece of aluminum food container, the disposable kind, up the chimney so that it blocked maybe half of the airflow. It didn’t seem to do much of anything to the draw when I operated the rocket mass heater after that.

How close to the floor of the final bell barrel is the exhaust to the chimney?

—The second bell is between the normal rocket mass barrel and the Mass. The exit of the stratification chamber is about 3 inches from the floor, I would guess, whatever height the pipe that goes through the mass starts at (as it gradually rises through the mass)

How tightly do you cover the J-tube feed between fires?


—I use two jumbo bricks, it seals pretty well, there are some gaps between bricks that I have filled in with a bit of Cob. it is not as good as seal as the metal prefab thing from the liberator though.


Do you have natural draft when the heater is cold?

—If it’s cold, as in cold-start cold, I don’t know, I would say maybe slightly. If it’s as in “cold in the morning,” there’s definitely a draw, I noticrd the difference when I was away for a few days and had to do a cold start, it was really hard to get it going. in fact, I removed my rudimentary baffle at that point, because I was worried that there was something seriously wrong, and I haven’t put that baffle back in again.


How strong is the draft when it is operating?

—I would say it is very strong, I don’t have much point of comparison, but it’s at least the same as the liberator was. Strong enough that it’s pretty easy to start the rocket mass heater. that aspect of this is way easier to use than liberator was.

As long as the main floor is not leaky (letting cold air percolate directly up), I think the underfloor insulation is not the main issue (but good to get it fully insulated).

—I’m doing the best I can. It’s a funky situation down there, lots of pipes and things to get in your way.  They’re definitely isn’t any leak, but it’s a tile floor, so it was kind of taking upon itself to radiate heat down into the basement, and I decided to put tinfoil under it as well as the insulation stuff.


A 6" duct in the mass would possibly be too quick of a reduction from 8", though the extra large barrel(s) above the riser may shed enough heat to make that not a problem. My experience with a 6" stovepipe and chimney from the bell of an 8" J-tube is good, but that has all the heat extraction in the zero-friction bell.

—Thanks for that information. So I think you’re saying that it should be OK, as long as a lot of heat gets shed before it goes into the Mass, right? And now I hope it is clear that there are two opportunities for Heat to be shed, the initial barrel, which is 1 1/2 barrels, and the second barrel that is a stratification chamber.  

My question is still if I should put the baffle back in and make it even more baffling. Claude the AI said to put 5 1-inch diameter holes in a circle of metal, which would be a pretty extreme baffle. Was Claude hallucinating?


A few other points, I have almost finished, coughing around the stratification chamber, but not completely.

I have put a “Cob hat“ on top of the first barrel, by which I really mean a gigantic aluminum animal feed tub filled with water. I haven’t measured its temperature, but it definitely has not gotten up to boiling. Which leads me to think that the top of the riser is not close enough to the barrel, to really shed the kind of heat you want to shed in this situation, and that would be a better optimization. I also have a metal tub on top of the second stratification chamber, and that one is about the right temperature for fermenting animal feed, which is nice, but I also wish that it got too hot, that would be a nice problem to have, which I could solve by putting another layer of bricks between that stratification chamber and the feed fermenting tub. These tubs can hold maybe 30 gallons of water.

Thanks so much for your help, I really appreciate it!

Some information we need to assess the situation would be the size and character of the house, its age, insulation, weathertightness, a description of the chimney...

What exactly do you mean by a baffle?


—I put a piece of aluminum food container, the disposable kind, up the chimney so that it blocked maybe half of the airflow. It didn’t seem to do much of anything to the draw when I operated the rocket mass heater after that.

How close to the floor of the final bell barrel is the exhaust to the chimney?

—The second bell is between the normal rocket mass barrel and the Mass. The exit of the stratification chamber is about 3 inches from the floor, I would guess, whatever height the pipe that goes through the mass starts at (as it gradually rises through the mass)

How tightly do you cover the J-tube feed between fires?


—I use two jumbo bricks, it seals pretty well, there are some gaps between bricks that I have filled in with a bit of Cob. it is not as good as seal as the metal prefab thing from the liberator though.


Do you have natural draft when the heater is cold?

—If it’s cold, as in cold-start cold, I don’t know, I would say maybe slightly. If it’s as in “cold in the morning,” there’s definitely a draw, I noticrd the difference when I was away for a few days and had to do a cold start, it was really hard to get it going. in fact, I removed my rudimentary baffle at that point, because I was worried that there was something seriously wrong, and I haven’t put that baffle back in again.


How strong is the draft when it is operating?

—I would say it is very strong, I don’t have much point of comparison, but it’s at least the same as the liberator was. Strong enough that it’s pretty easy to start the rocket mass heater. that aspect of this is way easier to use than liberator was.

As long as the main floor is not leaky (letting cold air percolate directly up), I think the underfloor insulation is not the main issue (but good to get it fully insulated).

—I’m doing the best I can. It’s a funky situation down there, lots of pipes and things to get in your way.  They’re definitely isn’t any leak, but it’s a tile floor, so it was kind of taking upon itself to radiate heat down into the basement, and I decided to put tinfoil under it as well as the insulation stuff.


A 6" duct in the mass would possibly be too quick of a reduction from 8", though the extra large barrel(s) above the riser may shed enough heat to make that not a problem. My experience with a 6" stovepipe and chimney from the bell of an 8" J-tube is good, but that has all the heat extraction in the zero-friction bell.

—Thanks for that information. So I think you’re saying that it should be OK, as long as a lot of heat gets shed before it goes into the Mass, right? And now I hope it is clear that there are two opportunities for Heat to be shed, the initial barrel, which is 1 1/2 barrels, and the second barrel that is a stratification chamber.  

My question is still if I should put the baffle back in and make it even more baffling. Claude the AI said to put 5 1-inch diameter holes in a circle of metal, which would be a pretty extreme baffle. Was Claude hallucinating?


A few other points, I have almost finished, coughing around the stratification chamber, but not completely.

I have put a “Cob hat“ on top of the first barrel, by which I really mean a gigantic aluminum animal feed tub filled with water. I haven’t measured its temperature, but it definitely has not gotten up to boiling. Which leads me to think that the top of the riser is not close enough to the barrel, to really shed the kind of heat you want to shed in this situation, and that would be a better optimization. I also have a metal tub on top of the second stratification chamber, and that one is about the right temperature for fermenting animal feed, which is nice, but I also wish that it got too hot, that would be a nice problem to have, which I could solve by putting another layer of bricks between that stratification chamber and the feed fermenting tub. These tubs can hold maybe 30 gallons of water.

Thanks so much for your help, I really appreciate it!

Two more wrinkles –

– The riser is more like 40 inches instead of 36. The burn tunnel was made too long, by mistake, so the builder compensated.

And then the barrel is more than 2 inches above the top of the riser, whereas Erica and Ernie’s book recommends 2 inches. That would seem to mean more turbulence and less heat transfer from the top of that barrel, so potentially more Heat would go into the stratification chamber? And then more out the chimney than we want?  The uninsulated part of the exit chimney feels like maybe 200°. The meat thermometer gives a reading up 130 Fahrenheit(but that’s not necessarily super accurate.)

Bump. AI is recommending that I put an extreme baffle in, is that to be trusted?  

Another factor that I should mention is that the rocket mass heater is downstairs a two-story house, so radiant heat maybe heating up here that is gradually conveyed upstairs overnight, such that the drop-in temperature in the downstairs room is more because of that, then a lack of performance. I can try putting the thermometer upstairs for a while to see how we’re doing up there, but I have been hearing some complaints of”it’s too cold up here”

So, asking for a friend...the rocket mass heater has only a twelve foot cob bench,, because of code reasons, and a 6" duct through that.  

It has an 8" j tube with an extra high barrel and extra large--65 gall, plus 8" off a second barrel, and that's in addition to the manifold.

But wait, there's more!  Act now and get half off your next bell.

There's a second bell for a stratification chamber (to compensate for the short bench) and this has been mostly covered with cob on the sides, about 2" .  (My friend is running out of clay but can get more in a few weeks).  The top has a tub of water in a big aluminum cauldron with a lid, maybe 20 gallons, it's squat and almost fills the whole barrel top with its girth.  It reaches temperatures of maybe 130 F after a burn.  

There's no cob hat on the first barrel but there could be...but it does have a metal "bonnet" of sheet metal curved over to reflect some heat back toward where it's needed instead of just heating the ceiling there.  (The ceiling has not been complaining about the cold).  

The bench gets only slightly warm.  The draft may still be too strong.  

The room goes back down to about 55 degrees rather quickly (ie overnight).  

The insulation situation between the first floor there and the. basement is still kind of sketchy--my friend has insulation but fitting it in around ducts and figuring out of how to remove ceiling panels has not yet occurred.

There is a crude baffle in the bottom of the exit chimney.  It could be more baffled.  (I, on the other hand, am almost fully baffled already.)

8" J tube with 6" duct shouldn't be a problem because of Charles's Law, the temperature has gone down from over 1000F to 300 by that point, and also because Uncle Mud said so.

I like to be able to cook on the top of the main barrel, including a tall pot of stew, but I'm wiling to let that go if I must, I could put a cob hat where there never was a hat.  (If you get that reference that makes me happy.)

What would you prioritize?

Do you agree that a baffle is helpful?

What else am I missing?

Thanks, team.

7” in. From Paul’s gesture it looks like he’s saying you put angle iron going one direction and then another layer of it across that, 90 degrees to the first layer. So forming a grid as viewed from above. That makes a lot more sense than the picture I had in my head from just listening to the podcast. And that’s more angle iron than I have, but I think some angle iron supplemented with the barbecue grill will do the trick.

https://www.youtube.com/live/qs-83fcwTWQ?si=blE1yJmUS6BzKvIH

I figured it out!  If I click on Paul’s YouTube channel and then click on “livestreams” it comes up.

Joshua Myrvaagnes wrote:Does anyone have a link to the YouTube live stream of this podcast? There are some visuals that would be helpful. Stones sitting on angle iron? Would a barbecue great serve as a reasonable replacement, how do you balance stones on angle iron, do you need to be able to levitate objects in order to accomplish this feat?

The search algorithm on YouTube is just not cooperative, I found out that there were about 5 million different people hawking different brands of wood stoves.  

Does anyone have a link to the YouTube live stream of this podcast? There are some visuals that would be helpful. Stones sitting on angle iron? Would a barbecue great serve as a reasonable replacement, how do you balance stones on angle iron, do you need to be able to levitate objects in order to accomplish this feat?

The search algorithm on YouTube is just not cooperative, I found out that there were about 5 million different people hawking different brands of wood stoves.