Glenn Herbert

It is common to have the feed tube about twice as high as the system dimension (in US terms, 8" system and 16" feed, floor to top), as this is the standard firewood length. Other countries may have different, even multiple, standards for firewood. Starting from a widely available wood size will make operation easier. You want the firewood to fit completely inside the feed tube so you can cover it and smother the flames in case of emergency. Also, double the burn tunnel height gives a vertical intake draft, which then has a sharp 90 degree bend to introduce beneficial turbulence and gas mixing.

15cm is about equal to 6". I would make the feed height at least 30cm, which is still very short. Do you have a strict limit on how tall the riser can be? I have found that 1:1.5:3 works fine in my 8" system. The actual dimensions of my feed and burn tunnel are 7" square, per first-generation RMH advice to keep cross section exactly equal, before it was widely known that a square is functionally equivalent to a circle of the same diameter for gas flow. A 30cm feed and a 90cm riser would still be very compact; even 40 and 120 is not very tall.

I think a chimney cap damper would depend on the situation. For a larger flue like 8 x 8 or more that a fireplace would have, it could be very useful even if the bottom was closed off. For a 6" diameter flue, air might not be able to circulate within the height of it so a top damper might not make a difference. An exterior chimney would get cold full height whether or not it had a damper on top.

The chimney cap damper would be to completely close the top of the chimney to keep it from getting very cold when not running.

My father and I did that when I was a teenager to close off a fireplace. We made a hinged metal flap on top of the chimney flue, with a piece of iron pipe running down to the fireplace throat. We would reach up inside the fireplace with a poker and raise the pipe end and set it on the throat shelf before starting a fire. With a ranch style house, it was easy.

I would invite you to make an example of your idea (in your back yard, not inside) and see how it works. To be sure it is fully effective, you would need professional testing equipment with sensors that tell you exactly what the heat and chemical output is... but if you can get it to burn totally smokeless after startup, and leave no charcoal whatsoever after burning is done, you might have a usable concept.

The heat riser (what you have called the burn tube) generates a strong draft. If it were horizontal, that draft would have to come from a very good chimney and building layout, which cannot be guaranteed. Designers have come up with some horizontal cores (Matt Walker is a prime example) which work well as long as they are built exactly as designed, and connected to a good chimney.

Part of the efficient combustion comes from restrictions or sharp bends in the flame path, which again must be built exactly as designed to work.

Batch boxes run best at full speed, and should never be throttled down. There is no need to throttle a batch box that has mass connected; you just run a larger or smaller load, or two loads in extreme weather, and the heat is stored to release slowly over hours or days. The colder your climate, the thicker you make the thermal storage walls so that heat takes longer to escape and overnight heating is more even.

On studying the SECMOL incinerator article, I note that is only around maybe 10" diameter (hard to tell for sure). It achieved up to 2000 F (1100 C), with a rather crude construction. Note that the riser is entirely ceramic fiber, and the base is clay bricks which will get fired nicely at the temperatures they are achieving.

Do you have a good quantity of wood or other easily combustible material to sustain the incineration of more problematic or erratic materials? You would want a good clean hot burn going before introducing plastics.

That is a gigantic J-tube! The dimensions generally scale proportionally, though at such sizes, I don't know if anybody really knows how it will perform. As there is a lower limit around 4" where the combustion to surface area ratio causes excessive losses and reduced temperatures, there may also be an effect at much larger sizes where temperatures get so high that you approach blast furnace conditions, with temperatures far above 2000 F. I would absolutely expect even stainless steel to be degraded quickly, and perhaps even melt.

You will need to use only refractory materials in your core. I don't know how your lava rock behaves, though I suspect it will start melting by 2000 F. Also, temperatures around 2500 F or so cause nitrogen to burn, creating NO2 and similar compounds which are harmful. You really don't want temperatures much over 2000 F. The highest grade firebrick I know of is rated for 2600 F.

Generally, the feed tube is the lowest temperature zone, with the later burn tunnel and lower riser the hottest. I am not sure how air velocity through the core will scale; I don't think it will be fully linear, as in three times faster than in an 8" J-tube. Thus, there may not be an advantage in making a 14' tall riser aside from the chimney draft effect. I don't think the horizontal burn tunnel needs to be fully twice as long as the feed depth. 28" diameter as you show is so huge that I think you would need industrial engineering and materials to construct and operate it safely. Even 12 to 16" square would have a very large capacity and high temperatures for incinerating.

What kinds of material do you want to incinerate? What size is the largest thing you would need to put in? What volume per day would you be burning?

For the riser, it needs to be one single cross section, not split up, as that would introduce more friction and slow the system.

Rather than trying to hold the trash in a drum, I think it would work better to make a firebrick "grate" of closely spaced fins standing up some from the floor, with the slots following the airflow streamlines so they get swept out by the draft. What would be the minimum common size of items in the load? Spacing to hold most of those up would allow good flow around the load. Fins/slots running down the sides of the feed might work well to get airflow around the load without dead spots.

For this application you would need a pump. The smallest one you can find would probably work fine, as long as it can handle hot water. Cast iron is generally cheapest, but with an open system it would corrode fairly quickly, so you need bronze or stainless steel.

If you wanted to heat a floor or anything above the stove tank, gravity circulation would work fine. Large piping makes circulation easier.

Nice ideas, but many of them are not really techniques used in medieval times in Europe. I have studied medieval domestic architecture for decades, and there are few if any references to them in publications.

Large windows with glass were not a thing aside from upper class dwellings in later period. South facing windows were not a regular practice, but might exist where convenient.
Animal quarters in or adjacent to the house were only common in certain poor regions, early period, or where essential to survival.

Underfloor heating by stones heated in the central hearth would require structural features that are not in evidence in any European context. It would require massive continuing effort to work in practice. Korea had and still has the ondol, with a firebox under one end of the house and smoke channels running beneath the raised stone floor. The Roman hypocaust essentially fell out of use with the fall of Roman civilization. Masonry stoves were developed in the 16th-17th century and later in eastern Europe as firewood became scarcer.

Stone walls are excellent in areas with large daily temperature swings, but in European winters, they would just be a constant heat sink. Wood and wattle and daub are okay as insulators, but not major help in keeping warm in leaky houses. Cob would actually have some degree of insulation value. Wall hangings in upper class buildings helped keep heat from being lost.

Brick or stone floors were generally upper class, and wood on ground floors was not general practice. Absent money for masonry, the ground floor was ground, with rushes spread for comfort.
Thatch is a good insulator, and if done right can last for generations. Its major drawback is fire spread, which caused it to be banned in many cities.

Enclosed beds were a later or upper class development, and certainly helpful.