What is the difference between a RocketMH and a RussianMH?

I am interested in understanding the difference between a rocket mass heater, and a Russian masonry heater.

So far I have:
- RocketMH are funky looking (recycled materials and homemade looking), and RussianMH look traditional and old-world looking (stone, mortar and brick).
- RocketMH easier to disassemble, clean and replace parts, and RussianMH don't really need to be disassembled, cleaned, or be repaired.
- RocketMH is DIYable, and RussianMH requires hiring someone (or does it??)

What I don't know:
- What is the fundamental difference from a science standpoint? Is it just stylistic, but they are from a science standpoint the same thing?
- Is one more efficient in terms of wood volume to BTU output?
- Is one safer?
- Is one more environmentally friendly?
- Other pros and cons?

Re building a Russian/Finnish mass heater youself: This guy says it can be done, but the detailed plans and materials used are not included in the article.

https://www.motherearthnews.com/diy/building-a-russian-woodstove-from-bricks-zmaz97onzgoe/

This is a Russian Masonry Heater:


source

This is a Rocket Masonry Heater:


source

Traditional masonry heaters (Russian and others) typically have a vertical orientation, and involve a circuitous path of exhaust gases through the mass before reaching the chimney. Older versions may or may not have a highly efficient combustion core, but even the least sophisticated are pretty good. The newest versions are probably the same efficiency as a RMH.

Rocket mass heaters are actually a subset of masonry heater; they more often have a horizontal orientation, though many newer ones are vertical and use a bell rather than a circuitous duct. RMHs are commonly built with free local or recycled/scrounged materials, but can be built of masonry the same as a traditional style heater. The essential difference is the rocket combustion core, whether J-tube or batch box, with its heat riser to keep the gases contained and hot until combustion is complete, and incidentally add some lift to aid in draw.

I'll go a step further and say this.  A Russian Masonry Stove is going to use a buttload of brick.  Much of it expensive firebrick.  A good deal of skill is going to be demanded of anyone who wants to put one together.   There is a great deal of complexity in the brick layout. Be prepared to cut a lot of brick.  Plans are available online for free.  

A Rocket Mass Heater will only need a fraction of the firebrick and/or other refractory materials.

The rest can be Clay and Sand, Some rocks, Tiles, whatever you can throw together for the mass.  Options are many and open ended.  Skill isn't as much a pre-requisite as is perseverence and perspiration.

Thomas has a good point. Clay/sand is almost free. Bricks are not, unless you're a 5-star scrounge, and even then you would have to transport them.

The Mother Earth bit I linked earlier (which may be from 1975, who knows) said:

He was familiar with the design we had gotten from the library. He said it worked, but it was too light in a few places. He recommended we put another complete layer of brick around the outside. This made the already large project much bigger. But, his rationale seemed justified, so we did it. Total bricks needed now: 1,900.

1900 bricks? Maybe it was just that design. Phew, I don't know how many of those had to be fire bricks vs. scrounged chimney bricks, but that's a helluva lot IMO.

Thank you everyone! Such cool info and perspectives!

Glenn Herbert wrote:...RMHs are commonly built with free local or recycled/scrounged materials, but can be built of masonry the same as a traditional style heater...

You were the first to say it on this thread, and I think this is the most important difference! I think the real innovation of the RocketMH is **the ability to do it yourself cheaply**, which makes them **economically democratic*. My lightly educated guess is the availability of modern ducting and barrels (a global supply chain container) allowed a redesign with horizontal runs and cheap materials that would not have been feasible or practical a couple centuries ago when the first ones were made. The science and the method are not new, but the DIY with found materials method DEFINITELY is new. The horizontal runs in particular which would have required many skilled steps, and likely difficult-to-find high quality clay centuries ago, are literally a snap of the fingers with mass-produced ducting/pipes. The less important differences are the RuMH is built to last, and has some legit aesthetic advantages. But the CO$T of them!!! 😲

Having been to rural arctic Finland and seen some of the handmade Finnish batch burn/mass heaters, I know the designs are all over the place, and they are not all made of the same materials, and some of them appear to have horizontal runs (although I couldn't see inside, so...) I also believe (I didn't say know) the RusMH are burning wood gas, because without that, these things (which cannot be disassembled and cleaned) would fill with creosote and catch on fire. The one thing I can say with confidence, is the pictures I find online of RusMH, and what I saw in person are a different - but I am hardly an expert. I have never been to Sweden, or Russia. I have four brick and stone masons in my family, but I have never owned either a RoMH or a RuMH.

A fun fact I learned over there is the Sami are the last native peoples using some traditional skills in Europe. The rest of them just asimilated modern ways as they came around, and lost that identity. Being part Native American, that blew my mind.