Glenn Herbert

I saw the original about 18 years ago, and was never sure if it was legitimate. I printed it out, but lost the last page, so am glad to see it complete to show friends.

You would want a smooth, gradual reduction to reduce the throttling effect. I would say that an 8" to 6" reducer 6" long would probably be enough.

The notion that big companies answer solely to their owners'/stockholders' bottom lines is accurate, but taking all that value and giving it to the workers immediately would cause chaos and most likely a coup. Applying the proposed laws to new companies only would probably place them at a fatal disadvantage, unless there were some method of gradually transitioning and pressuring existing companies to make it advantageous to switch modes. Thinking of actual ways to create incentive for a transition via regulation would be more useful than just proposing a completely unworkable sudden shift.

I tend to agree that voluntary cooperative action to implement the donut model of economic thriving instead of growth is vanishingly improbable. However, eventually something like that will occur because it has to on our finite planet, and it may well be because economies trying to grow endlessly break down and slowly collapse, with massive disruption to every measure of wellbeing, until the world perforce retreats to a sustainable level of activity. I think it likely that this will coincide with a dramatic drop in human population to a globally sustainable level, by all kinds of unpleasant means.

It is true that decreasing population does not necessarily have to be catastrophic; as someone wrote, if each year two out of a hundred people you know died instead of one of a hundred, the total population would become a small fraction of the original in a century.

You mentioned dimensions being a bit smaller than they should be by the book... I have found that there are the standard commercial firebricks exactly 4 1/2 x 9 x 2 1/2, and a skimpier version about 1/4" smaller in each dimension. At least you don't have a mix of the two - that would be a real hassle to work with (don't ask me how I know).

It's not ideal for the burn tunnel to be only 6 1/2" tall instead of 7", but that is the one place in the system where a slight constriction is said to be okay. I think if you just add a layer of splits laid flat around the top of your feed, after building up the surrounding material so they can be well bedded, you will get a nearly exact 16" height which will work fine. This would give a nice flat hard surround to your feed. If you are custom cutting all of your firewood and want to make it all about 14" long, that would work too.

I think ensuring the gasket fits correctly is the trickiest part of removing and replacing either a barrel or a lid, and there would not be much difference in the time and care involved. It would just take some more muscle to lift the whole barrel over the riser. Another factor: if you want to closely inspect the riser or other parts or make any repairs, it will be easier to do with the whole barrel off.

I did use some metal in my RMH, but it could be avoided easily. I have a masonry and cob bell, which could be done in all cob (but with less safety and code compliance).
Rocket mass heater with 8" J-tube and bell

My steel feed insert could be replaced with a firebrick feed easier and cheaper... I wanted to try it for the p-channel supply and air preheating; it works very well, but is not essential to operation.
An access panel to inspect the riser is a really good thing, but could be done much more simply than mine if you are not concerned with "living room" esthetics.

For fast and complete burning, a pocket rocket should do the trick. A standard barrel and a couple of lengths of stovepipe is all you need.

Yes, as long as the (plastic) bags are isolated from the heat. Typical earthbags might not be suitable, as their thickness would make for many hours' delay in heat getting through to the surrounding space, I think the part of the wall that forms the RMH container would need to be more rammed earth than earthbags, to get proper wall thickness and heat resistance. You would want a noncombustible lining for the bell enclosure.

What you are describing doesn't sound like any kind of rocket combustion unit. To get the combustion efficiency and heat output of a rocket stove, you need specific geometry (there are several proven styles) and an insulated combustion zone. Even if you are just mainly wanting a burner to get rid of waste biomass, you would want to burn it completely and not generate pollution. (There is another important point of why you would burn biomass instead of composting or otherwise turning it directly into improving your soil.)

A regular exhaust pipe or muffler would not allow enough flow for a fire similar to your picture to burn well - one principle of rocket stoves is that the cross sectional area is relatively constant throughout the stream. You need fast enough flow after the initial combustion point that the gases experience turbulent mixing, and all the fuel gases can meet oxygen and burn.

https://permies.com/t/41635/Top-Questions-Rocket-Mass-Heaters

http://donkey32.proboards.com/thread/1170/tube-dimensions