Gonna start my first RMH soon. I have some questions.

Denny.

You should have thought about the specifics.

He wants to use a masonry chimney as mass. If the wall is half outside, it will heat up the birds. Your case is different. You're making a RMH. Not a batch rocket with a bell.  Still, if the bench is against an outside wall, remember to insulate bellow and against the wall, to avoid conduction to the outside world. And BTW, nobody told you yet, that a bassement RMH isn't worth much?

Satamax Antone wrote:Denny.

You should have thought about the specifics.

He wants to use a masonry chimney as mass. If the wall is half outside, it will heat up the birds. Your case is different. You're making a RMH. Not a batch rocket with a bell.  Still, if the bench is against an outside wall, remember to insulate bellow and against the wall, to avoid conduction to the outside world. And BTW, nobody told you yet, that a bassement RMH isn't worth much?

Ok I see. I shouldn't have to insulate my walls they are underground. I did just read about the basement deal.  I kinda figured it would be as efficient. That is why I built it so far from my flue,  so that it's in the middle of the house. It's sitting right next to the basement stairs. I am gonna durock the ceiling down there so that it pitches toward the stairs sending all the heat up.

Denny, few details.

on this pic, you show the "plenum"



I think it would be good if you enlarged the hole. See https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

And i would also cut the top of that pipe lengthwise, except for it's mating end; Raise two sides of that cut to weld under that barrel lid, for a bit more depth. Which would accommodate more fly ash. And obviously make a plug to use as a cleanout.





What length of pipe, and how many elbows do you have there?

https://permies.com/t/59302/Length-exhaust-pipe

A chimney on an outside wall can function, but loses much more heat than an interior chimney, so is more liable to creosote buildup or poor draft.

Regarding your bench ducting: Unless you use the basement regularly for living space, a bench is less than optimal for heating the upper floor. It needs to be heavily insulated from the floor so you don't lose a lot of heat to the ground. In any case, a tall masonry or cob bell will radiate heat closer to the upper floor where it is needed.

If you do keep the bench, I would say that the duct run is considerably too short to extract most of the heat. A 6" J-tube is supposed to be good for around 30' of horizontal run, with elbows counting for 5' each. I do note the slope to the chimney, which might be partially counted in length. But a bench this size may not store as much heat as the system can generate. If you plan for the basement stairwell to be the main heat avenue, I would ideally move the core to a few feet from it and surround the core with a tall bell, and run the exhaust from the base of that about as you currently have. Heat would have to move the least in this scenario, and be directed more to where it is needed.

Satamax Antone wrote:Denny, few details.

on this pic, you show the "plenum"



I think it would be good if you enlarged the hole. See https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

And i would also cut the top of that pipe lengthwise, except for it's mating end; Raise two sides of that cut to weld under that barrel lid, for a bit more depth. Which would accommodate more fly ash. And obviously make a plug to use as a cleanout.





What length of pipe, and how many elbows do you have there?

https://permies.com/t/59302/Length-exhaust-pipe

I will check out that post. My exhaust is a 6" sprinkler pipe t. One side I'm making a plug for it as a clean out. There is 5 elbows and 5x 60" pipe with two clean outs one at exhaust and one in that corner before it rises to the chimeny.

Glenn Herbert wrote:Regarding your bench ducting: Unless you use the basement regularly for living space, a bench is less than optimal for heating the upper floor. It needs to be heavily insulated from the floor so you don't lose a lot of heat to the ground. In any case, a tall masonry or cob bell will radiate heat closer to the upper floor where it is needed.

If you do keep the bench, I would say that the duct run is considerably too short to extract most of the heat. A 6" J-tube is supposed to be good for around 30' of horizontal run, with elbows counting for 5' each. I do note the slope to the chimney, which might be partially counted in length. But a bench this size may not store as much heat as the system can generate. If you plan for the basement stairwell to be the main heat avenue, I would ideally move the core to a few feet from it and surround the core with a tall bell, and run the exhaust from the base of that about as you currently have. Heat would have to move the least in this scenario, and be directed more to where it is needed.

I see what your saying about the bench to small. I'm trying to take everything you all are saying to make this work pretty good. How about I make the bench an L shape and on the corner of the L make a bell there to hold more heat? You think that would be pretty good.

You can build a steel core as you originally planned BUT rather than insulating it, you MUST air-cool it! Whenever steel gets over 900F it will glow red hot and corrode very quickly! RMH temps far exceed this but air-cooling on the exterior will enable you to avoid overheating your steel core. See my 7" steel air -cooled RMH at  https://permies.com/t/69632/Building-tube-steel-air-cooled for more details on safely constructing a steel cored RMH that will last.

Of course, if it's air-cooled rather than insulated, it's not going to reach the temperatures that make for such complete, clean combustion and probably means it doesn't count as a rocket core at all.

Bruce Woodford wrote:You can build a steel core as you originally planned BUT rather than insulating it, you MUST air-cool it! Whenever steel gets over 900F it will glow red hot and corrode very quickly! RMH temps far exceed this but air-cooling on the exterior will enable you to avoid overheating your steel core. See my 7" steel air -cooled RMH at  https://permies.com/t/69632/Building-tube-steel-air-cooled for more details on safely constructing a steel cored RMH that will last.

I decided to go with a batch box style. I'm still working on it.

Bruce, i'll put it bluntly.

Your thing is not a rocket. A fumivore if you want, but not a rocket. And it's getting on the nerves of several people here, that you're pushing your core on every occasion.

What would be good, is that you would report after two or three burning seasons. So we can see what your results are. Another good thing to do, would be to have someone with a testo, test it.

On another side. You don't need to push it so hard, you have nothing to gain. You have not reinvented the wheel. People have done it this way before you. And nobody will hire you to build one.

I wish you all the best.  But try to learn more here and on other websites, and give more convenient solutions than your metal thingamabob.

Bruce - on this forum, your air cooled metal core is NOT currently accepted as a rocket core.

If at any time the consensus of the RMH experts who advise the staff here changes,  we will let you know.

Well on a better note. Here's my progress.

My first layer give or take 2 1/2" thicker in the back, was potter's clay mixed with a lot of perlite 10 bags 8qt each. I couldn't find the big bags well I could but, wanted to get this part done this week and not wait for shipping.
Btw there was no mesh in it so it kept cracking as it dried and I kept filling gaps with more.

Next layer is clay and course sand about another two inches. I did put chicken wire in that layer. Let's see how much it cracks. It's taking a very long time to dry being in this cold basement. I have a fan right on it. The rest will be clay sand straw mix. Can I use hay?

That is the door I'm going to use on it. I may torch some more holes in it just gotta see how much air that one pulls. Gonna build that next because I'm going to bolt it down to the concrete slab.

Hope I'm doing an ok job.