Best place to put an RMH in a hexagonal pod home

This is my first post so I'll do my best to not waste anyone's time.
I've been looking at making Owen Geiger's modular pods home out of earthbags (pic related).
I haven't built the house yet, currently in the research phase. In the center of the kitchen is a wood stove for heating the house, but i would like to put a rocket heater in the house instead. Where would be the best place to put it? Also what would likely be the best type of RMH to build?
Each pod is 372 square feet for a total of 1,336 square feet.

Just so you know, the following information is based completely on what I've read online and logic.  I've never actually built an RMH.

Logic would dictate, because rocket mass heaters do not blow hot air into other rooms, that you would need a source of heat in each "pod".  (RMH ducts can be put under the floor to maximize space if you're not using a bell design).  I'm sure there are more clever solutions, though, that would enable a single RMH to heat the whole area.  Perhaps you could install radiant floor heat in all pods, connected to a single heater...  But then again, I have never heard of anyone doing something like that for such a large area.  And I lack the hands-on experience that would tell me exactly how far a heater could stretch.

As for a type of rocket mass heater, there's a lot of information online about such things.  I'm going to build one myself (soon, hopefully) and I've learned a lot about them -- or, more accurately, I've learned as much as I could from the online resources I've so far found.  There are two types of "feed" that I've so far encountered -- the regular ol' "J" kind and the easier-to-use (but more difficult to build) "Peterberg batch-box" kind.  J tubes are smaller (can hold less wood) and need to be tended quite often.  Batch boxes, in contrast, require much less tending for a steady fire (maybe twice or thrice a day) because there is enough space in the box to hold a lot of wood.  However, they need to be constructed out of firebrick or heat-resistant concrete, and the air intake usually requires welding.

Do some research to learn about them.  If you've already done research, do more.

Personally, when I finally build my own, I'm going to first try a "J" kind, to get a feel for building RMHs.  Seeing as I'm not going to have my own house (and workshop) for a while yet, the "J" kind is a better option for me -- no masonry to cut, no welding to do, and no cement to cast.  But the batch box looks much better for a house-heating option -- you won't have to feed it every 15-30 minutes.

There's another design decision to make:  whether to use a bell design or a flue design (I think it's also referred to as "contraflow," but not entirely sure).  There are lots of great posts about this already, and I can't pretend to know much about it (I'm just a seventeen-year-old sustainability nerd, after all, and not a mason), but here's a a site written by somebody who is:  Article  And if that didn't make sense, I don't blame you, and here's another:  Article

Basically, with a bell design, all the hot gases being put out by the rocket core go to the top of the "bell."  As they release their heat through the skin of the bell, they sink to the bottom and are replaced with new hot gases.  They exit through a hole at the bottom and possibly into another bell.  This ensures that only the coolest gases will leave the system, allowing maximum efficiency.  Besides, with a bell system, the gases are not as likely to "back up" into the house once the heater is warm.  Here's an article listing bell RMH projects built by experienced masons, including commentary:  Article  The site is a bit confusing, but you'll probably figure it out.

With a flue design, hot gases may or may not exit the chimney along with cooled ones.  Therefore, it's not as efficient.  However, it's unbeatably easy and cheap to build -- requiring no masonry skills and utilizing ductwork.  This is the kind of RMH you probably picture when you think of the term.

Anyways, just throwing ideas and information out there.  I hope the articles I've shared help at least a bit.  If I have any incorrect or disputed information in this post, I'd appreciate being told -- there are varying opinions on how to build these things.

As for recommendations, it really depends on how willing you are to work hard.  If you build a batch box rocket bell heater, you'll basically be building a masonry stove.  It'll be really nice, but it'll be difficult.  And if you have to build three of them -- well, let's just say that you don't want to have to do that.  Besides, if you want to save space by putting it in the floor, your only option is to use a flue design and probably a J tube.  

I wish you luck.

I'd eliminate the halls, in favor of a 4tg pod directly above (on the image) the kitchen and put it in place of the little seat I'm the kitchen. Youd lose the hallways but condense it all closer together

Heather Petersen wrote:
Logic would dictate, because rocket mass heaters do not blow hot air into other rooms, that you would need a source of heat in each "pod".  (RMH ducts can be put under the floor to maximize space if you're not using a bell design).  I'm sure there are more clever solutions, though, that would enable a single RMH to heat the whole area.  Perhaps you could install radiant floor heat in all pods, connected to a single heater...  But then again, I have never heard of anyone doing something like that for such a large area.  And I lack the hands-on experience that would tell me exactly how far a heater could stretch

It's my understanding that a RMH would provide plenty of heat for the entire house, I was more concerned about floor placement, possibly building a heated bench. The original provided floor plan shows a single wood heater, and an RMH is much more efficient, so I'd imagine it'd be an improvement in heating. Would you happen to have any ideas as to where in the central pod it should go/ what design to use? I'm considering putting the burner next to the right hallway and extending a bench down the wall all the way to the external door at the bottom.

Jon McLain wrote:I'd eliminate the halls, in favor of a 4tg pod directly above (on the image) the kitchen and put it in place of the little seat I'm the kitchen. Youd lose the hallways but condense it all closer together

I want to eventually combine six pods, which would favor the current floor plan. That fourth pod would have to be a bathroom, laundry, and closet, and I worry that'd equate to a waste of walls, plus I'd need to completely change the roof design because otherwise rain would pool in the center. Thank you for the idea though

If you lived in a colder climate than Georgia, I would say that the plan as shown is extremely inefficient and would be hard to heat, and would second the consolidation, moving the square areas to the north side and snugging the main rooms together. However, cooling is probably more of an issue for you.

I think the original woodstove in the center pod would not heat any more than that pod, the hallways and maybe the nearest bathrooms. It would do very little for the bedrooms except by hot air traveling along the hall ceilings and dropping into the occupation zone as it cooled, with a cool breeze heading back at ankle height.

A RMH could not do much better; it works mostly by line-of-sight radiation and conduction. The original plan is not designed to be heatable by a single source.

If you do want to try one RMH, I would put it in the center back wall where the couch is, with bell-benches extending half to 2/3 down each hall to bring warmth out.

How do you envision the additional pods connecting? That would impact the appropriate RMH layout.

I imagine the basic concept following the original floor plan to create a full hexagon, but I would put in another RMH. What would be an alternative to an RMH, since I would prefer not to use gas or electric? Or would it make more sense to just add another RMH? I assumed the designer of the house had taken heating into consideration..

A full symmetrical hexagon would make a huge house. If the three-pod design is 1336 square feet, the hex would be at least 3000, and that is interior space. If you roof over the central ring as one of Geiger's drawings shows, you would have something like 4500 square feet, which is firmly in "mansion" range. What kind of family or use are you considering ultimately? Thinking big is fine, but tempering it with reality is also good. With the thick walls (which I like), you actually have to build substantially more structure than you get to use, between roof and foundation and exterior finishing.

From a layout standpoint, a symmetrical hexagon would entail long stretches of hallway which don't do anything for you, and would encroach on separable spaces - one of the double bedrooms would be cut into, and the "office" space would be a wide spot in a hallway. You get much more effective use of your building efforts and expense by having spaces connected more closely.

I don't think there is any better alternative to a RMH for non-fossil active heating. You would need to add another one to heat a stretched-out house. Old European houses do often have two or more masonry heaters. Being in Georgia, I think taking advantage of passive solar heating would be quite effective; you could probably arrange to charge the massive interior walls to carry and moderate the spaces through cold nights in spring and fall, minimizing the need for fires.

Out of curiosity, what is it about the linked hexagon design that you like?  It seems to introduce a lot of complications that aren't present in rectangular buildings.

Glenn Herbert wrote:What kind of family or use are you considering ultimately?

I'm not entirely sure. I'm still figuring life out, and may decide to have a few kids, be a batchelor, etc. the idea of sharing a house with another family intrigues me though. I like this design because i can start with the right most two building on the three pod design and leave it that way, or expand as needed.

Steven Kovacs wrote:Out of curiosity, what is it about the linked hexagon design that you like?  It seems to introduce a lot of complications that aren't present in rectangular buildings.

I like the idea of a home being modular. there werent alot of designs i truly liked made by Geiger, but I'm having trouble finding floor plans by other designers.

J Howard,

Your thread here has actually reminded me of that 3 hex pod design. After some looking through Geiger's designs a bit again, I have decided to to use that same 3 hex pod design as a starting point for the underground home I want to build. I really liked the idea of a round home, but reality is round makes difficulties for furniture and hanging pictures etc. I really hate right angle boxes though. Hegagons are however really amazing shapes that are used throughout nature for very good reason. They are sort of a compromise between round and box, being neither but having benefits of both. Plus I have a hex 216 sq ft canvas tent. So a hex theme seems sort of nice.

Though I am now in the same boat as you trying to figure out how best to locate a RMH in such a structure.

Best way to sort of think of this design I think would be as if it is a Ranch Style house. Long and sprawling. So getting heat to circulate to the ends of the home if you centrally locate a RMH might be difficult.

I am still at the beginning stage of thinking of how to do things for myself, but two options have sort of popped up for me.

#1 supplementary heating. Adding a wood furnace to have the ability to do forced air heating to circulate warmth through out the home. There are some great wood furnaces, and many can double as a water boiler for heating domestic hot water.

#2 Multi smaller sized RMHs. Adding a 2nd or even 3rd RMHs. Having 2 on either end of the building, or even 3 one in each hex pod. Since kitchens tend to generate plenty of heat anyways, having 2 RMH on either end could be enough possibly.

If your going to have conventional roof, you will have an easier time than I will since you could possibly add new smoke stacks and RMH if needed. Since my plan is to bury my house I need to really plan out any and all smoke exits I plan to install. Though with my house being buried I also might have less need for as much heating, considering that is part of why I want to bury it. To gain the warm in winter cool on summer benefits of underground homes.

While this doesn't help your where to locate a RMH question, I thught I would share my rework and mod of the 3 pod design.



Something to note, is the greenhouses I added into the design might help me with some of the heating. Since they will collect some decent warmth that can hopefully be circulated to the far ends of the house. But I am still working on figuring out if I will want to add a wood burning furnace and if I might want to locate a RMH in the master bedroom. If you or anyone else wants to read more about my thoughts and plans for this design I have a more extensive write up in this thread https://permies.com/t/56342/Moving-Okanogan-homestead-land-pics#527590 I just don't want to derail this thread from the OP's question too much here, but thought he might enjoy seeing my mod of the 3 pod design.