William Bronson

Mark, you make an interesting point.


As I've followed the development over the years I've seen the consensus around chimneys shift.
In the early days many people insisted that a normal vertical chimney was not needed,now most people involved in the making of rocket mass heater seem to think it is best practice to use these kinds of chimneys.

Rocket mass heaters with good chimneys can still be subject to back draft.
A good insulated chimney is one thing that helps prevent that.
Heating that chimney also helps.
Most current designs call for a "bypass" that routes the exhaust gasses  directly to the chimney, "bypassing " the horizontal piping.
Once the chimney is sufficient hot , the bypass is closed and the exhaust gassed are drawn through horizontal flues that are buried in the thermal mass.
Once the thermal mass is hot enough, the heat it gives off is usually enough to create draft, meaning there might not be a reason to use the bypass except for when the mass is stone cold.


You mentioned the a simple firebox  in one place and the inevitability of  creosote production  in another.
The dimensions, geometry and material  of a properly built rocket mass heater create a burn intense enough that no creosote is produced.
Most of the research around rocket mass heaters centers on perfecting this part of the design, known as the core.
It's simple enough , in execution, if you follow the formulas laid out, but the designs themselves are not simple.



Because the fires in rocket mass heaters burn hot,fast, and clean, there are not a lot of points where hot coals are sitting unattended.
Because there is no thermal mass around a conventional wood stove, users seem to favor low smoldering fires for unattended heat.
In either case, hots coals and a back draft would be a disaster, but a rocket mass heater doesn't depend on smoldering
fires for long lasting heat.

Your posts make me think you might not know how the "bell"  form of thermal mass.
I've recently tried to explain the principles of how a bell works and  seemed to fumble it rather badly , so I'll leave that to someone else.

Light straw or fiber adobe seem ideal for SIP.
Anything heavier like traditional cob or adobe seems like it would weigh to much.

I have a hard time imagining a RMH costing so much, but then again, I am a compulsive scrounger.
I also put function over form, so ugly is very subjective.
A stove that's a little crooked or made with bits of salvage that saves my family a bunch of money is gonna look beautiful.

There are thermostatic valves for radiators that might work:
https://en.wikipedia.org/wiki/Thermostatic_radiator_valve
I don't know if they exist for 3" pipe.

There are  also thermally activated actuators  used to open and close greenhouse vents.
They could be fitted to a pipe plug instead of  a greenhouse window.

I am one of those guys who is held back by insurance fears.
My fears are furthered because I want I avoid scrutiny from my insurance company.
I have a visceral fear of any kind of consequential  paperwork, and I have been following news of people losing their house insurance from simple drone flybys.
All that fear is reason enough for me to focus on other life challenges.
Not reasonable, but there it is.

The only cost that concerns me is the flue.
Although rmh can operate without a chimney, they work much better with one.
Although they can use single wall stove pipe or maybe even even HVAC duct, local codes might call for something much  more expensive.
My own home has one chimney with two flues.
One was made for the new fangled first floor gas fireplace, the other for the basement coal furnace.
Either should be fine as is for rocket stove exhaust, but I'm pretty sure local code calls for a stainless steel liner.

Before I found permies I learned about thermal mass heaters that were located in the cellard of off grid cabins.
It was just the basic barrel stove, buried in literal tons of rock and earth and burned as hot/ quickly  as possible.
I have considered doing this with the cheapest conventional woodstove that will pass regulatory inspection.

M Ljin, you make a great point.
Just reflecting the light towards the plants or soil  could be an improvement.
Foil covered foam is common and cheap insulation used to block car windows.
If it were applied to the northside (or south, depending on where you live)of an east to west  greenhouse, it's liable to be a net gain in retained energy.

If we just put reflectors behind or to the right or left of a greenhouse, we could increase solar gain,but  outside the greenhouse these would be subject to wind and snow.

Picture a tall  A frame green house, 12' on the north side 10' on the other, 10' on the bottom.
The 10' side will be at about 73 degrees  facing south.
On the 10' sides we put clear glazing.
On the 12' side that we form a parabolic reflective trough, focused inward.

I think the focus point will be at around 54" up from grade, but we could make the parabola asymmetric, to focus it lower in the greenhouse, but 40 gallon water heaters are about 60" tall.
Plumb them together and run a loop through the planting beds.
Circulate your water with an inline pump.

Because the interior of the A frame is about 9 1/2' tall at its height, we can use clear plastic to make a smaller space inside of it, effectively giving us double glazing.
Normally the space high up in an A frame is hard to use/justify ,but in this design it would collect extra solar energy.

Theoretically, there will be no more energy collected with a solar concentrating collector than with greenhouse surface of the same size.
In practice I think heating a smaller mass to higher temperature could be very useful.

I immediately think of heating air in a tube and directing that air into a solid mass under the roots of the plants you are trying to grow.

Because water holds a lot of heat and we have lots of infrastructure for moving it, heating water and irrigating with it seems like good idea.
That could be very simple, down to leaving a big pot to boil and pouring into the irrigation reservoir.

Ok, so this guy was inspired by the Anila stove.
I don't like his loading/unloading mechanism, but I do like the blower separated from the burn chamber.
He reports that it takes 4 hours of burn time to pyrolize the feedstock, and described feeding the fire during that time.
That sounds terrible to me, but there is some differences in planned uses and designs between he and I.

I want an all in one fuel + charcoal feedstock cartridge that can be swapped in and out of an outdoor boiler.
The ease of loading and unloading is important to me, because I hope to be heating my house this way  in my old age.
If he filled the center cylinder I think it would hold less than a 1/2 gallons of fuel, compared to to the nearly 4.5 gallons of charcoal feedstock.
I think a ratio of fuel to feedstock of 1 to 3 would be reasonable, assuming the feedstock looses a third of its volume during pyrolosis.

For context, a roughly 6" diameter circle has about a 4th the area of a 12" diameter circle, so a reactive stove with a 6" dia inner cylinder and a 12" diameter outer cylinder would have that 1/3 ratio.

I'm putting some bits together to build a stove.
No holes cut yet, just messing about.

The plan to use to stainless steel bolts and nuts to affix the silverware holder in the middle of the stock pot.
Air admittance and control, yet to be decided.

The lid is a pizza pan, inverted over the bean can and affixed with self tapping screws.
With a hole saw, we punch a 2" hole through the pan and into the van.

In use, the outer ring is filled with  any old feedstock.
The lid goes on, the bean can slips directly into the silverware holder and is filled with pellets or charcoal.
The center is a tlud, the outer ring a retort.
Light it off and hopefully it makes more char than it uses.

John C Daley wrote:

 soilcrete walls

William what are these please?

Well Soilcrete uses onsite dirt for the aggregate in concrete.
I've not found many examples of 'soilcrete" in walls but cast earth, or cement enhanced adobe all  seem to be similar.

Here's a Permies thread about it:Soilcrete