Under Floor RMH

I like the idea of a subfloor or crawl space basement rmh to heat the floor etc., it seems to be all about venting and cement

Cheers

What would be the benefits?
- Less space used inside?
- would you feed it through the floor?
- would you build the house over it?

I also like this concept. More-so undeground. I learned about RMHs about 8 hours ago. I've read about RMHs for about 8 hours. I need to sleep on the info and let my brain figure out the questions I have and the end goal of my build. Just saying hello and thank you all for the shared knowledge.

We shall heat the world.

Okay, I'm ready to start asking questions now. My goal is for the feed opening to be level with the ground and the burn chamber undeground. Please don't take my measurements as EXACTLY literal, that will be refined later when all the kinks have been uncovered and addressed, the measurements are just to help our imaginations draw a picture:  I'd dig about 20 inches down by 20 inches wide and about 12 ft total length. I'd build the system in this area using brick, ceramic fiber board, and sand and other most suitable materials eventually topping it with a layer of brick or pavers. The only part I want to be above the ground is the riser and the barrel. I would like the barrel to be surrounded by a latticed brick cube (or cylinder shape if I get crazy) hopefully it would get warm to pretty hot, but not REALLY HOT. I would like to use this cube/cylinder as a table off center in the Tipi. I have small children so my goal is for nothing REALLY HOT to be touchable (with the exception of the feed opening that l'll probably step in....ugh). I plan to then put a granite or marble slab on top the cube/cylinder to even further lessen the top surface heat. This is hard to type while keeping my fingers crossed that this is even possible....

I would like to build a stove core out of Ceramic Fiber Board and FireBricks very similar to what Luke at Rocketstovecores.com has created. And then support that with brick and then backfill with sand so everything is comfy cozy undeground.

I want to go with the smallest size functional, my desire is for the top of the table (riser + barrel + surround brick cube/cylinder) to be 3ft or less ABOVE ground. I'm thinking this part might be where my wishes cause problems


The lattice structure of the surrounding brick cube/cylinder would hopefully allow lots of heat to escape and lots of airflow around the barrel as I'm thinking that's important to keep the barrel from getting too hot and therefore reducing the effectiveness of the draft. Some science about temperature differences between upflow in heat riser and down flow in barrel from what I understand.

Then the exhaust would go undeground and either chimney up outside the Tipi if the extra draft is needed or it can go straight out like in the terrible drawing as I do have a small ledge there.

Please tell me if this seems possible and what considerations I should make?

Thank you all!  I promise to take lots of really nice pictures when the build begins. And also have tons of questions as I go along.

SERIOUS THANKS in advanced, I've already learned so much from all of your contributions on here.

UPDATE: I think I'll aim for a 30 gallon barrel, that will allow ample room for the brick surround to be distant enough that it doesn't get too hot.

Also to note: the fire would never be burning for prolonged periods of time, I assume that eventually the bricks would get VERY hot but the longest the fire would burn is a couple hours to kick the cold at night or in the morning if it's terribly cold out.

Waco Dandy wrote:I want to go with the smallest size functional, my desire is for the top of the table (riser + barrel + surround brick cube/cylinder) to be 3ft or less ABOVE ground. I'm thinking this part might be where my wishes cause problems
Please tell me if this seems possible and what considerations I should make?

Yes, it's possible and has been done before. Building below grade means a specific set of requirements are to be met.

#1 All parts of the heater that're underground need to be heavily insulated. That is including the horizontal pipe that is leading to the outside of the tipi.

#2 You'll need a real insulated chimney of three or four yards high, a horizontal outlet won't work in most (if not all) circumstances.

#3 There's a common understanding that a 6" system is the smallest that'll reliably work, 4" is definetely too small unless there are special tweaks incorporated.

In all, a 6" J-tube, insulated all around, buried in the soil. A barrel that's placed on the soil with the lower ridge packed around with some mud would be airtight enough. The ground under your tipi is a giant heat sink, the thing won't work at all without insulating the horizontal pipe. The same goes for the vertical pipe, it need to be insulated in order to overcome a cold start.

One way to cheaply insulate such a chimney is this: take an 8" stainless steel stove pipe, and put 1" Morgan thermal ceramics superwool at the inside. Once that is properly done, slide a 6" steel stove pipe inside and you'll have an insulated chimney. Do this piece by piece and place those on top of each other when done.

Bricks around the barrel can be done, just dry stack those against the barrel. It won't get hot enough to burn one's skin. One 55 gallon barrel is less than 3' high, placed direct on the ground.  OR bite the bullet and build a brick bell around the riser, without barrel at all. This'll provide a mass which stays warm for hours after the fire is gone.

For a riser: please take the 5-minutes riser into consideration. That consists of an 8" stove pipe with superwool inside (no steel pipe inside the wool this time), placed on the core of the J-tube. It is compact, heat resistant, highly insulative, quickly done and durable at the same time. One has to take extra care of mounting it in such a way that part of the steel pipe, however small, won't be in direct sight of the fire. It'll corrode away in short notice when that's the case.

Thank you, this is the kind of information I'm looking for. I'll work on gathering materials and would like to dry build it above ground and fiddle with it before excavating and burying it.

Would everything work with a 30 gallon drum to give me a smaller overall diameter once the bricks are added?

Thanks for the thorough and complete response. Once I start putting things together I'll upload images.

I tried to sleep in the Tipi last night and confirmed my desire for a heat source. 26° is not good for enjoying sleep.

Thanks again!

Okay I'm hoping for clarification on the need to insulate the underground portion. Isn't the point of all the earthen material built around the above ground models to act as a heat sink?

Is the concern with the underground that it would just pull away too much heat?

Additional question: what's the general range of heat I should expect for the gasses at the point where they leave the barrel and enter the exhaust ducting?

Thanks.

Hi Waco;
The earth is the hugest heat sink there is.
If you do not insulate completely, instead of your tipi staying warm, the earth will suck it all up and then take more.
Forget using a barrel and use clay brick, it will stay warm versus the barrel which will cool quickly.
The transition temps should be 300F-500F

Thank you Thomas, I'm okay with losing the heat that is absorbed by the earth from the exhaust line (I would of course enjoy the slightly warm pavers for bare feet that lay on top of the line), but my focus is using the heat generated at the barrel (now clay bricks, thanks for that advice). Do I NEED to build the bricks in a circular fashion around the heat riser for proper functionality? or would a square/cube work just fine? I'm not sure if the barrel shape facilitates some kind of vortex or something?

I'm excited that this is panning out so well. Thanks!

I think you need to insulate the fire box in order to generate maximum heat and combustion, if you dont insulate the heat will travel through the brick and into the soil rather than radiate back into the firebox.
If that happens you wont get much draw and the system will fail.
Perhaps the most efficient rocket stoves are made purely from insulating material, with no brick at all, but they have a few disadvantages, mainly in that most available insulating products are soft and get damaged, or they are not good for your health.
So a more usual method would be to use thin fire brick backed with insulation.

Okay thank you, that's what I was thinking. I'll insulate the heck out of my fire box, fire bricks then ceramic fiber board, then more bricks. That way I maintain good combustion temperature there. It's crazy difficult to source any local fire brick rated above 1500° or any ceramic fiber board. Sad to ship in such bulky heavy items. I'm keeping my eye out for local soapstone slabs I can cut to use as an alternative.

Thank you for info.