My first RMH, a removable one

Hi there, here are some pics of a rocket that i have been making at a friends place. We tried to run away from the hobbit look that usually goes with Rocket mass heaters we've found on the web.











It is still not finished, but it is burning really good, specially aftger correcting the intake size that was too small to properly fire up the dragon.

the full gallery is here: https://plus.google.com/u/0/photos/112030274594483704018/albums/5827925415331196705

Hope you enjoy our work!

Best regards from Gaia, Portugal!

Great work! I think this project is one a lot of people will be watching. I will be interested to know what kind of mass you use and how well it retains heat. Also let us know how well the stove fire box works. I have seen several questions about using a wood stove mated to the rocket bell. Chris

That's a super clean looking build, can't wait to see the finished product!

Couple of questions: Is that a built in oven on the side, or is that your burn chamber, with the black tube on the left side your air inlet? If it's the burn chamber how long does it take before you have a smoke free fire? It seems like heating all that wood at once with a restricted air supply would cause a lot of smoke unless there's another air inlet somewhere.

What do you plan to use for the thermal mass in the bench? From what I've been reading, it seems like there have been some problems with using a loose fill in an enclosed frame like that so I'm interested in how you tackle those issues if you come across them.

Looking forward to seeing a burn video, keep us posted.

I agree, its a nice build.
Is that copper tubing running into the heat riser?

Hats off to you.
Such a pretty build.

I am surely no expert on this at all. I am wondering what is the temperature of that exhaust flue as it enters the wood box? I am thinking quite possibly you may have to replace the wood surrounding it by something with insulation value.

Looks great. What is that which you are using instead of a 55 gallon drum?

Hi guy's, thank you for the nice feedback.

@Laura: yes, we are using rockwool at the crossings between boxes and between the first unit and the thermal mass ones. We are using a scrapped air compressor reservoir. It is quite thick, about 3~4mm, but works great.

@Paul: yes, the copper runs inside the heat rizer embedded into the insulation. We use a mix of refractary cement and ash for that and a couple of metal tubes to act as a mold. It will be used to power a classic open vent setup.

@Michael: The inlet is in fact that metal pipe in the pictures. The box is the burn chamber. What kind of issues should we expect with the wood boxes? Stress from the filler material as it heats up and expands? I thought about that but since i had found nothing on such issues was going to see the results and cope with them. Thanks for the heads up, but specificaly what issues are you refering to?

About the inlet, we are still evaluating a couple of options and it goes along these lines: two inlets, one directly from the outside and another from the room air; one bigger inlet replacing the existing one taking room air; one bigger inlet taking exterior air.
The elements at stake/balance are: heat loss, interior air quality, eficiency.

About the smoke, since we haven't actualy changed the air inlet, i can't say nothing except that in the testing it smoked a lot when i opened the door, so i grabbed a hair dryer and placed it at the inlet and it started burning vigourously and smoke free instantly. The design of the closed burn box retains all smoke untill you open the door. It's air tight, just like any modern closed fireplace. After about 5 minutes i removed the hair dryer, the burning slowed quite a bit but smoke free. After changing the inlet we'll see the results


@chris: we where thinking of using plain ash. It's a lot of ash, lol!

The temp of the exhaust air is 600F and the exhaust tube might be even hotter, but not as hot as the burn chamber (3,000F).
What happens to glued wood particle, and the "paint" on the wood at 600F, esp while the exhaust tube and wood are physically touching.
I know that the sawdust in the regular clay bench burns.
So I would say at least a huge amount dangerous chemical vapours from the paint and glue and possible even a fire.

While both ash and clay are both insulators. I think clay has a higher density thus it can hold more heat in a smaller volume.
So as long as your "bench" has a big enough volume ash should be fine.
I also think that the ash will stay hotter for longer, which is always a good thing.

Im not sure if i understand correctly.
You plan to use ash as thermal mass? Thats not a good idea. Ash is used as insulation material, it has low mass too. So its kinda the worst material for that.

Also that rockwhool might be too soft for the horizontal surfaces. As i said, for thermal mass, you want something heavy. And if a heavy object compacts your insulation it will not insulate much anymore.

The wood have too little clearance from the exhaust pipes, to play it safe make bigger holes and put some insulation between the pipe and the wooden parts.

here is the gallery link: https://picasaweb.google.com/112030274594483704018/RMH?authuser=0&feat=directlink it changed because i left google plus.

Thanks for the feedback Balint and Bengi.

I recall reading somewhere that it was a great material for the bench. I also recall seeing somewhere around this forum a table for the heat transfer characteristic of several materials, can't find it anymore. Anyway, i was going for the cheapest material i could find. I didn't knew that there was a relation between body mass and thermal mass, are you sure about this?
The rockwool was applied at the corner where the distance between the exaust pipe and the box panels is smaller, but since there is a substancial space filled with air(inside the tube), the weight on the critical zone will be small. The clearance is just enough to fit a nice 30mm layer of rockwool.


When we finish it and start using it daily, it will be sorted out quickly

To me wood ash is basically soil particles once all the carbon, water and nitrogen has been burnt off. http://en.wikipedia.org/wiki/Wood_ash
So it just less dense soil aka clay with no/little organics matter.

Here is a link with thermal mass and volumetric thermal mass info. http://en.wikipedia.org/wiki/Specific_Heat_Capacity

Could you give a materials list for this. Especially interested int he door construction.

Door was made with scrap metal, a piece of tube, a refractary cord 2 small hinges and an L shaped piece. The lock was made from a couple of pieces of scrap junk.

The vitroceramic glass was expensive, costed 40 euros.

The metal tubing of the flue was 66 euros, 2 pieces straight tube 2 45 degree curves and 2 T's.

I don't have a bill of materials as most of them were collected here and there, and the final cost would had been more significant if we had not managed to get a lot of scrapped or reclaimed materials.

Bricks where about 1 euro a piece of the new ones(about 50), some other were scrapped from various sources, and had diferent sizes what complicated things.

Copper tubing was found at half the price(don't ask the price because i can't remember).

Black Ram wrote:here is the gallery link: https://picasaweb.google.com/112030274594483704018/RMH?authuser=0&feat=directlink it changed because i left google plus.

Thanks for the feedback Balint and Bengi.

I recall reading somewhere that it was a great material for the bench. I also recall seeing somewhere around this forum a table for the heat transfer characteristic of several materials, can't find it anymore. Anyway, i was going for the cheapest material i could find. I didn't knew that there was a relation between body mass and thermal mass, are you sure about this?

Very sure. You store heat in mass, not in volume. Heat capacity is different for each material, but it is still given for unit weight of the material.
Heat transfer (insulating property or conduction) is important too, for if we insulate around the pipe, the hot gases just not going to give the heat to the heat battery and just leave the building hot. Ash is insulating material. People use it around heat risers just for that. I guess one could compact it to hell, and then it might become somewhat dense, but its just too much, too dirty work. (and a lot of material) I would use soil instead, if you have trouble getting clay and sand.
A side note here. The glued wood thingy might not like water, particularly in steam form. It might deform, swell or become soft for a while. The plastic on its surface can protect it though, but i advise you do the first drying runs until the thermal mass is not sealed, so as to let steam escape easier.

I still don't like the wood stuff. I think some of it will pyrolyze in extended use. I burnt stuff like that, its very stinky, try it yourself, not good...

Sorry for digging out this topic so long after, but only discovered it now.
I am also from Portugal - could we chat about the RMH?
Thank you



It is still not finished, but it is burning really good, specially aftger correcting the intake size that was too small to properly fire up the dragon.

the full gallery is here: https://plus.google.com/u/0/photos/112030274594483704018/albums/5827925415331196705

Hope you enjoy our work!

Best regards from Gaia, Portugal!

Hi Jose;  Welcome to Permies!

We love to talk about RMH's.
Were you hoping to connect with the original poster? Or were you wishing to just ask questions?

The original poster has not posted anything in 6 years. I do not know if he could be reached.
You could attempt to reach him with a purple moosage here at Permies.
Simply click on his name. This will take you to his bio page. At the top right you will see an envelope. Click on it.
This will take you to the message page. Try to connect with him and see if he responds.
I do know there are other folks in Porgual who have working rmh's.

Rather than add on to an old post.
Try starting a new post about your questions.
Simply go to the rocket mass heater forum and click on " new topic" This will open the reply page.
Ask your questions and hit submit.