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

Hi I'm new here. I've watched a bunch of videos of the heaters and tried to get some measurements together. I do have some questions. I'm putting this thing in my basement.

1. I'm gonna make the heat riser steel, 6" id with a wall thickness of almost 1/2". Then a 8" steel pipe over it with a wall thickness of 1/4. In the middle of the two I'll stuff ceramic wool. They will both be 4' tall.

2.  I want to make the burn chamber and feed inlet steel also. I have access to steel for an awesome price. I figure I will completely cover the burn chamber in cob for insulation or I can wrap it with ceramic wool and then cob over that.

Other than weight does anyone see a problem with this?

I have a diagram I drew that I will share with you all and see what you think.

Thought about even changing the burn chamber to a 4x5

Denny Romero wrote:
Other than weight does anyone see a problem with this?

Yes.  The steel is going to burn out at the sort of temperatures reached in a rocket mass heater.  

Check out this thread - using metal in the burn tunnel and heat riser

What does the temp in it usually reach?

Burra Maluca wrote:

Denny Romero wrote:
Other than weight does anyone see a problem with this?

Yes.  The steel is going to burn out at the sort of temperatures reached in a rocket mass heater.  

Check out this thread - using metal in the burn tunnel and heat riser

Ok just read thru another long post with a lot of information on this heat problem with steel. Back to the drawing board gotta figure out how to build the heat riser now. Thank you for shooting my idea down. It made me read more into it. I would have never thought that it was gonna get that hot in there.

Yes Denny, no steel or concrete until you move away from the core.  Also having your horizontal pipe rise is not necessary. A 6" core should be 5.5" x 5.5" square all the way thru. Some people will make them 5.5 wide and 6.5 deep to allow for an inch of fly ash to settle.  If you don't have one you should buy the "builders guide" by Ernie & Erica Wisner  all of the specs and the reasons behind them are explained.  Consider a riser made with fire clay and perlite using a 16 gal grease barrel as an outer form and a piece of round concrete form (sonitube) as a burnout inner form. This works great ! I have been using this method since my first build... reused my original on 3 cores before the outer grease barrel failed.    Buy the book... Read it cover to cover ... ask any questions here!  Build your RMH and ENJOY the warmth!

thomas rubino wrote:Yes Denny, no steel or concrete until you move away from the core.  Also having your horizontal pipe rise is not necessary. A 6" core should be 5.5" x 5.5" square all the way thru. Some people will make them 5.5 wide and 6.5 deep to allow for an inch of fly ash to settle.  If you don't have one you should buy the "builders guide" by Ernie & Erica Wisner  all of the specs and the reasons behind them are explained.  Consider a riser made with fire clay and perlite using a 16 gal grease barrel as an outer form and a piece of round concrete form (sonitube) as a burnout inner form. This works great ! I have been using this method since my first build... reused my original on 3 cores before the outer grease barrel failed.    Buy the book... Read it cover to cover ... ask any questions here!  Build your RMH and ENJOY the warmth!

Thank k you for the reply. Your riser looks amazing. I'm gonna try and make mine out of fire brick. Not that I don't like your it's just that I have a 280 gal wood stove in the basement that's been there for 25 years and the whole bottom of it is lined with fire brick. I just took one out and it's in great shape. Gonna see how many I can get out of it. It's time for that thing to go the creosote it produces is insane. I would say there has to be around 100 bricks in it.

Did the math. There should be 66 bricks in there.

Ok ignore the mess but my rocket stove will be setup all the way where the shelving is on the right. The bench will be there too. My exhaust will go at an angle all the way to the exhaust that the wood stove is in, in the chimney. I may have to mount some kind of shelf along the wall so that I can cob half way up the pipe. That way the little ones don't get burnt.

Free fire bricks are always good ... I replaced a Victorian era  coal/wood burner ... what a wood hog / creosote maker it was. The temp of that pipe after the mass will be apx. 130 F  hot but not hot enough to hurt.   Just right to teach about hot things to little people.  

thomas rubino wrote:Free fire bricks are always good ... I replaced a Victorian era  coal/wood burner ... what a wood hog / creosote maker it was. The temp of that pipe after the mass will be apx. 130 F  hot but not hot enough to hurt.   Just right to teach about hot things to little people.  

Yeah it is I was looking at the prices of fire brick.....wow.

With firebrick it matters where you are looking for them.  If you look in main stream box stores they are horribly expensive! Sold as wood stove insert replacements.  If you look at a masonry supply you may find that the heavy bricks   are apx 2.00-3.00 each  split bricks are a little more and the insulated bricks are more yet.  

thomas rubino wrote:With firebrick it matters where you are looking for them.  If you look in main stream box stores they are horribly expensive! Sold as wood stove insert replacements.  If you look at a masonry supply you may find that the heavy bricks   are apx 2.00-3.00 each  split bricks are a little more and the insulated bricks are more yet.  

Good tip. I know a potter that has them big light bricks for about 3 bucks each but now I hope I won't need any.

Can I use this busted cinder block in the mass? Also here's my brick stacked up burning the creosote off of them. I'm gonna have to buy a couple more.

Yes, busted concrete is called "urbanite". There should be NO air pockets in your mass so each piece of urbanite must be placed and covered by cob before the next piece.  Consider getting some of the insulated bricks for your burn tunnel and riser.

thomas rubino wrote:Yes, busted concrete is called "urbanite". There should be NO air pockets in your mass so each piece of urbanite must be placed and covered by cob before the next piece.  Consider getting some of the insulated bricks for your burn tunnel and riser.

Ok cool. Insulated? I know the top row isn't fire brick but the others are the heavy fire brick. Is the insulated ones the light ones?

Thank you by the way.

Yes , The lite ones from your potter are insulated firebrick . Ideally your entire core and riser , excepting the feed tube  would be build with these . The heavy bricks steal heat away from your burn until they are thoroughly hot... the lite insulated bricks do not get hot so they allow the heat to travel thru the system, for a better burn.  The feed tube is built with heavy brick to resist wear while putting in firewood.

thomas rubino wrote:Yes , The lite ones from your potter are insulated firebrick . Ideally your entire core and riser , excepting the feed tube  would be build with these . The heavy bricks steal heat away from your burn until they are thoroughly hot... the lite insulated bricks do not get hot so they allow the heat to travel thru the system, for a better burn.  The feed tube is built with heavy brick to resist wear while putting in firewood.

Ok makes a lot of sense.  On more question on the cob. I live in nc where we have this red clay dirt. I called the landscaping place to see if they had clay dirt and they said they only have the red fill dirt. I even asked them if they knew what cob was and they acted like I was crazy lol. So my question is can I use this kind of dirt for it?

thomas rubino wrote:Yes , The lite ones from your potter are insulated firebrick . Ideally your entire core and riser , excepting the feed tube  would be build with these . The heavy bricks steal heat away from your burn until they are thoroughly hot... the lite insulated bricks do not get hot so they allow the heat to travel thru the system, for a better burn.  The feed tube is built with heavy brick to resist wear while putting in firewood.

Wow pricing the insulated fire bricks. There's no way I'm going to be able to replace all of them. I'll talk to a potter here where I get my ceramic wool and see if he has any uses bricks for a cheaper price. Even if I can get the back or the burn chamber and lower riser with those.

Insulating firebrick are ideal for the job, but very pricy as you found. Perhaps the labor of building a perlite-fireclay riser makes more sense now...

Glenn Herbert wrote:Insulating firebrick are ideal for the job, but very pricy as you found. Perhaps the labor of building a perlite-fireclay riser makes more sense now...

Yes it does.

N.C. has clay, you just need to find it.  To start with you may be able to purchase 50# sacks of powdered fireclay... in Spokane it is $10 a bag. Ask your potter or a masonry supply house for it.  As for regular clay there are two easy places to check . First is your county road crew may have a good idea where you might be able to dig clay. Next ask any building contractor who is "digging" they will no doubt have free bucket loads of clay... Or  just go out in the woods near a creek, chances are you will find clay.  Heck some back roads have mud holes that are not only clay but clay and sand with the proper consistency for cob...   If you have good pure clay you will need as much as 3 times the amount of sand to clay ...   So bring home sand, lots of sand  (not from the ocean its too fine) as well as clay. If you choose to purchase sand it should be builders sand .

thomas rubino wrote:N.C. has clay, you just need to find it.  To start with you may be able to purchase 50# sacks of powdered fireclay... in Spokane it is $10 a bag. Ask your potter or a masonry supply house for it.  As for regular clay there are two easy places to check . First is your county road crew may have a good idea where you might be able to dig clay. Next ask any building contractor who is "digging" they will no doubt have free bucket loads of clay... Or  just go out in the woods near a creek, chances are you will find clay.  Heck some back roads have mud holes that are not only clay but clay and sand with the proper consistency for cob...   If you have good pure clay you will need as much as 3 times the amount of sand to clay ...   So bring home sand, lots of sand  (not from the ocean its too fine) as well as clay. If you choose to purchase sand it should be builders sand .

Ok nice I'll have to talk to the potter I'm sure he can send me some where and get a trailer full of it.

Here's what I have so far. I'm gonna buy about 15 more insulated bricks and put them down in the bend. The front metal door will be for putting bigger logs in there and clean outs. It's welded to the metal frame and the bricks slide right under it. The bottom of the steel plate gets warm so I think I'm gonna leave it open to store wood under it. I have to see how hot it will get when everything is sealed up.

What do you all think so far?

Here's the inside.

Denny,  that's  very nicely built ... looks really good... Sadly the heat generated at the bottom of the feed tube is going to warp it in no time

thomas rubino wrote:Denny,  that's  very nicely built ... looks really good... Sadly the heat generated at the bottom of the feed tube is going to warp it in no time

Hopefully it won't warp. Burnt it for a while today and the screw knob was warm but cool enough to unscrew it by hand. When burning there shouldn't any fire in that little metal box. Unless your talking about the metal base? I hope that doesn't warp lol I welded a 2x2 frame around the bottom hopefully it's enough to hold it from bowing to much.

What is your plan for permanent installation? What kind of floor structure is there? With the core so high in the air, it would be more difficut to connect it to a bench for mass and seating, and also possibly less convenient to reach down in for cleaning.

A big steel box like you have on the front will leak a lot of heat from the core right where it should be insulated. My experience with a J-tube only slightly larger than yours is that it is easy to scoop ashes with a sardine can mounted on a short handle, no need at all for a cleanout. I only clean ashes once a week or so, everything is reduced to mineral ash, no coals. I think the idea that long logs put in the front will burn well is misplaced... the steel box part may not keep heat well enough for that end of a log to burn completely, and flames from the part sticking all the way down the burn tunnel may not have time and turbulence enough for complete combustion. Logs sitting flat on the floor will get less than ideal air contact for complete combustion, just like a conventional woodstove.

Glenn Herbert wrote:What is your plan for permanent installation? What kind of floor structure is there? With the core so high in the air, it would be more difficut to connect it to a bench for mass and seating, and also possibly less convenient to reach down in for cleaning.

A big steel box like you have on the front will leak a lot of heat from the core right where it should be insulated. My experience with a J-tube only slightly larger than yours is that it is easy to scoop ashes with a sardine can mounted on a short handle, no need at all for a cleanout. I only clean ashes once a week or so, everything is reduced to mineral ash, no coals. I think the idea that long logs put in the front will burn well is misplaced... the steel box part may not keep heat well enough for that end of a log to burn completely, and flames from the part sticking all the way down the burn tunnel may not have time and turbulence enough for complete combustion. Logs sitting flat on the floor will get less than ideal air contact for complete combustion, just like a conventional woodstove.

My plan was to install it just like that and cob around the whole core even half of that metal box in front. As for the bench I was gonna run the 8" exhaust pipe down the back almost to the ground. The floor it will be sitting on is the basement concrete slab.

Glenn Herbert wrote:What is your plan for permanent installation? What kind of floor structure is there? With the core so high in the air, it would be more difficut to connect it to a bench for mass and seating, and also possibly less convenient to reach down in for cleaning.

A big steel box like you have on the front will leak a lot of heat from the core right where it should be insulated. My experience with a J-tube only slightly larger than yours is that it is easy to scoop ashes with a sardine can mounted on a short handle, no need at all for a cleanout. I only clean ashes once a week or so, everything is reduced to mineral ash, no coals. I think the idea that long logs put in the front will burn well is misplaced... the steel box part may not keep heat well enough for that end of a log to burn completely, and flames from the part sticking all the way down the burn tunnel may not have time and turbulence enough for complete combustion. Logs sitting flat on the floor will get less than ideal air contact for complete combustion, just like a conventional woodstove.

On The warping issue that I may have. What if I replace all the bottom bricks to insulated fire bricks? You think maybe that will help keep the heat off that plate?

Denny ; When a J tube is up and roaring , the bottom of the feed tube is glowing orange... any wood you drop in bursts into flame immediately...  That's very hot, 456 F is burning point on wood... for a room temp piece of wood to burst into flame ... i'm guessing 1000 F +  My temp gun won't go high enough.  That is the kind of heat generated at the feed tube...  What will this do to plate steel ?  

In a J-tube, the feed tube and floor of the burn tunnel get the most abrasion and impact, and benefit the most from being hard firebrick. Everything else is better being insulating material.

It would be beneficial to make a layer of perlite-clay a couple of inches thick on your base plate before setting the floor bricks, both to protect the base and to insulate the core. At least 2" of perlite-clay all around the core will help it get hot enough for excellent combustion.

Glenn Herbert wrote:In a J-tube, the feed tube and floor of the burn tunnel get the most abrasion and impact, and benefit the most from being hard firebrick. Everything else is better being insulating material.

It would be beneficial to make a layer of perlite-clay a couple of inches thick on your base plate before setting the floor bricks, both to protect the base and to insulate the core. At least 2" of perlite-clay all around the core will help it get hot enough for excellent combustion.

Ok so I couldn't afford to buy all insulated fire brick. As for the bottom I kinda took your advice and bought enough hard fire brick to put an extra layer on the bottom. The j tube is burning extremely hot and roaring for all the gaps I have I can't wait to set it up in the basement and really seal it up. I will take the advice and put the perlite-clay around the combustion chamber when it's put together. Here's some pics of the fire brick layout I'm gonna use. Gonna work on the barrel and exhaust port today.

Should I go with 8" exhaust or 6"?

Ok so watching it burn today what I'm going to do is cut the legs off my frame to get the exhaust closer to the ground like someone mentioned. Gotta get the paint off this barrel it won't burn off. I don't think it's burning as hot as it can right now because nothing is really sealed. Decided I will go with a 6" exhaust. I have to make a cap for that one side as a clean out. The lid to the barrel is welded to my frame so all metal pieces won't move when I take it down stairs and the just stack the brick back around it.

Here's some pictures. I'll take more pictures later.

Here's updated pictures

I put a paper in the tube oh man the draw is amazing

Ok it's done other than cob. I'm going to test for a couple of weeks before I cob it in. Also gonna put durock on the ceiling slanted to the steps to send all the heat up stairs. The door is cut in two and I can open just the top and cold air drops down the two vents. What do you all think?

Denny Romero wrote:Ok it's done other than cob. I'm going to test for a couple of weeks before I cob it in. Also gonna put durock on the ceiling slanted to the steps to send all the heat up stairs. The door is cut in two and I can open just the top and cold air drops down the two vents. What do you all think?

    Hi Denny! I built something like you did a couple years ago in my basement as well. I'm only going to offer you some advice, and I don't wan't to sound like I'm bashing or discrediting you in any way. I simply have already made some of the mistakes that you have. So, before you put any cob on your stove, here are some words of advice that will save you time and a bit of head-scratching. #1 Take the drum off, take it outside and completely remove all of the paint. #2 The barrel lid that is in contact with the heat riser is going to burn out, you need a proper manifold that will be farther away from the riser. As a plus, this will grant you a way to lower the exhaust duct, and get it closer to the floor. With the exhaust duct closer to the floor, you wont need as much of a bench. The big bench that I had in mind when I built mine was later found to be a big waste of time. The floor and walls of your basement are going to suck all of the heat out anyway, and my bench never got even close to being warm. These days I have no bench at all. #3 Are you going to insulate the core and riser? 1" of refractory blanket is recommended. #4 I have had bad results with metal in the wood feed, I would build that up with firebrick.

I merged your stuff with the following thread. I hope that is okay by you.

Satamax Antone wrote:Daniel, i would say, it's perfectly possible.

We need to know more about your fireplace and chimney.

Is the back of it against an outside wall? If yes, that's a bad point.

What is the section of your chimney at my be 4 ft above the fireplace floor, 10 ft? 20 ft? Just to see if it could be used as a bell. Single storrey house, or is there levels above?

Would you mind loosing some space in front?

Is that carpet on the floor? Wood underneath?

Are you able to lay firebricks?

Are you really willing to do this?

Have a read of this, and the links. https://permies.com/t/68801/Conversion-conventional-fireplace-rocket-mass

And tell us what you think.

Sorry to high jack but why can't the chimeny be an out side wall? I'm asking because I'm building mine in my basement and it's going to a chimney that's an outside wall here's a picture.