As far as a thermometer goes, you need a thermocouple. You have choices as far as how high the thermocouple probe can read; the higher the temp, the more expensive the thermocouple. The thermocouple probe is on the end of a wire and the display is on the other end of the wire outside the kiln. You can order them off ebay from China, wait a few weeks, and save some money.
We live in the gulf coast area (just North of Houston). We have not tried Prunus hybrids. However, we have tried a Plum tree. When it has a few fruits on it, they are delicious. But, it gets confused because the tree requires a low number of chill hours. Even the peaches will bud and blossom too early.
We also have a nice apricot tree, some blossoms, but NO fruit.
The chill hours are the problem. You have to have low chill hour trees for a warm winter, but if the winter is cold, you get nada.
We have had great success with citrus, peaches, and pears. If you live near the gulf coast, you should have Bob Randall's book.
A main advantage of the terracotta chimney flue liners is their structure. They are self-supporting.
We have a chart on our Dragon Heaters blog which addresses the thermal mass issue. Cob vs. terracotta not much difference from a conductivity and heat storage point of view. Terracotta flue liners have to be insulated from temperature changes greater than 50°F per hour. So, we recommend lining the first bell with standard fireclay brick splits (1.5" thick). The fireclay bricks do store heat better than cob or terracotta, so that makes the castle build more like a masonry heater. Fireclay brick material has the best price/performance for conductivity and heat storage.
Cob makes the working environment slick which can result in injuries or falls when walking around. We are not fans of cob.
We are using Peter van den Berg's design for the J-tube rocket heater; we have tested its efficiency and published the results. (You may be able to find the sketchup drawings of his J-tubes on line.) His design burns so efficiently there is no build-up of creosote or soot. Our designs recommend installation of a cleanout door for use once a year to get rid of ash at the bottom of the bells.
We have a chart with the relative BTU's per hour of the 3 sizes of burn tunnel which we sell. You need to know how many BTU's are needed for your house.
IMHO, the 4" needs to be tended way too often in order to keep the burn going. I would recommend a 6" because of this issue.
have seen some posts suggesting that you could adapt a larger system to a smaller flue, but couldn't find anything definitive.
Here is a definitive answer backed up by experimentation. If you have an 8" system, you can't use a 6" stove/chimney pipe. It won't burn properly; you will get smoke back and end up covering part of the feed tube to make it work.
The exhaust system must match the size of the combustion system or be larger...not smaller.
Technically, the steel drum is not tall enough relative to the heat riser to be an effective bell. If you want to read more about bells, there is a document on the blog in my signature which compares and contrasts bells vs. flues. A traditional rocket mass heater as described in the book is a flue system; the exhaust is routed through a constricted space and stratification by temperature does not take place to any significant extent. In a bell system, plenty of space is provided for the exhaust to stratify by temperature. The warmer gasses which were involved in the combustion stay in the bell until they have given up their heat to the surface of the bell. The cooler gases, such as Nitrogen (which is 79% of the air), fall out quicker and are swept out of the chimney.
My understanding of your question is: at what point in the combustion system is the temperature the hottest? Is it at the top of the heat riser? The bottom of the heat riser? The end of the burn tunnel?
In order to really say what the temperatures are inside a j-tube combustion system, someone would have to build it with thermocouples wired into place. The thermocouples which can handle the temperatures inside a burn tunnel are relatively expensive. One must also have a display/recording device on the other end of the wire.
On the other hand, if a particular combustion system does not have visible smoke that would indicate that somewhere in the combustion system, the temperature is reaching 1,200°F. This is the temperature required to consume the volatiles which normally appear as smoke.
Would you like to share with us why you are asking this question? Perhaps someone can help you with the issue without having these particular facts.
The blog in my signature has an article discussing the contrast between the way the exhaust is stratified in a bell and flows all together in a flue, bells vs. flues. Bells have some advantages, although they are not part of a traditional rocket mass heater as described in Ianto Evans and Leslie Jackson's book.
If this is premixed fireclay in a pail and it runs about $1/pound, here is what I know. We recommend it as a mortar for the joints between chimney flue liners and as a way to attach fireclay bricks to the sides of chimney flue liners. We tell our customers that the joints should be no thicker than 1/8"; any thicker and they will show cracks and leak air when they dry. It dries very hard and brittle.
It is also a conductive material like dense fireclay bricks.
Cindie, you often speak out loud, but you still haven't tried rockwool?
I said that it may or may not handle the heat because WEB4DEB has a pellet rocket heater in which he wrapped his metal heat riser with rock wool. In his autopsy published on 2/22/2013 at minute 1:36 he shows how the metal is long gone and the rock wool has deteriorated significantly.
We used rockwool on the outside of the firebrick in our kiln, so it is a material which is known to us.
You might also notice that in the rocket they built at the workshop in MT recently, they used ceramic fiber blanket around the feed tube and heat riser areas of the combustion system.
Exhaust from a fire does not want to go down. It wants to go above the height of the fire. If you try to force it down, your fire will be smoky and not burn fast and hot.
The terra cotta pieces can stand the heat, but only if raised no more than 50°F per hour. Since a rocket heater gets hotter much faster than that, Santamax is recommending that you slit them and put some insulation around them for testing. The rockwool may or may not handle the temps making their way to the outside if used around the burn chamber of a j-tube. Ceramic fiber is the only thing which will definitely not disintegrate.
Is building on a hardwood floor ok? I think it is, but the question that follows is: how much insulation do I need? I have access to firebrick that I plan on using for this.
Firebrick is conductive and good for heat storage. What you need as a barrier to your wood floor is something insulative, like a 4" air gap. See p. 68 in the book.
I strongly recommend a chimney pipe. The burn is clean in the middle; but sometimes getting it going or when it is dying down, you might have some smoke or some tasteless, odorless CO which could kill you.
In the case of j-tube burn tunnels, smaller is harder to do. Peter van den Berg designed a 4" burn tunnel which does work and has the same efficiency numbers as his 6" and his 8".
Woodworking forums have ideas about drying wood. There are solar kilns with fans, for example. Moreover, I think your 20-30% is incorrect. Our air dried wood was 15% and I live in a very humid climate.
Cooking, like frying something, generally requires close control of the temperature. This is not easy with a rocket j-tube design or any wood-burning device, for that matter.
If your wood has moisture in it, it cools down the fire because the fire has to heat the water into vapor first before it can get to the wood. A cooler fire is less efficient at releasing all the BTU's stored in the wood. This would be true for any sort of wood-burning device.
On the other hand, while rocket stoves burn very hot and very clean, they are not efficient. Rocket stoves are hungry and consume lots of fuel."
If Kimberly stoves were so efficient, they would include a graph from a Testo 330 gas analyzer (or something similar) on their website; do they? They are really nice looking. It is also interesting that Kimberly is even comparing themselves to a rocket stove.
It would not be possible to burn clean and not efficiently. Burning fast and hot necessarily make the burn more efficient. What this person may be referring to is that a j-tube design creates a lot of heat, so you need to store it somewhere or your living environment will alternate between too hot and too cold as a cast iron stove does.
There lies the intersection of the rocket mass heater and masonry heater. Both of them have relatively small combustion areas and a large mass in which to store the heat.
Building a rocket design with a lot of metal parts would not tell you whether you would like a rocket mass heater in your house. Metal does not have good thermal storage characteristics.
People who have rocket mass heaters in their living quarters (including me) are very happy with how much heat they get for the amount of wood consumed.
The best compromise between price and performance on that chart is fireclay brick. The type being referred to in the chart is a dense fireclay brick weighing 7-9 pounds for a standard size brick. Or, you can acquire some castable refractory which has the same characteristics as dense fireclay brick. With fireclay brick, you don't have to worry about exploding water or spalling concrete.
If money is not a concern for you, choose soapstone; it is better looking.
If you have small children, please find an alternative to a bare steel drum. They can get 800°F; any contact with that temperature metal would do permanent damage to the skin.
Efficiency should be used to describe the amount of heat which is extracted from the wood during the combustion process. What you are discussing in this post is what to do with the heat after it has been created.
In a proper j-tube combustion system, combustion is complete after the exhaust leaves the top of the heat riser. Consequently, there shouldn't be any combustion in the top of the barrel.
I admit liking bells better than the steel drum/cob bench approach. If you store the heat in fireclay brick or cob, infrared heat is in play rather than circulation of warm air. This is a different basic principle from the forced air approach you might be using now. It is also more comfortable. A large warm object radiating heat in the middle of your space actually feels warm and makes controlling the warm air less of a priority.
Hope to also use some hydro mass with thermo syphon around barrel.
There are probably not enough BTU's to do both water heating and another type of mass storage.
You need materials which have good thermal conductivity and good heat storage. Many possible materials are included on a chart in a post called thermal mass on the blog in my signature. Dense fireclay brick material is a lot better than cob/clay in both of these areas.
My impression is that you are willing to spend some money on materials, if it will improve the performance. Do I understand you correctly?
Satamax is using the European equivalent of terra cotta chimney flue liners in those pictures, as far as I can tell. They can take the heat, but only so much at a time. So, we have designed some DIY builds which line the flue liners with dense fireclay brick for heat storage. Dense fireclay material does have better heat storage characteristics than cob. Our blog has a chart of materials used for thermal mass.
The EPA funded study says that if you achieve 100% combustion (carbon and gases from pryolysis) you will achieve just over 15,000 BTU’s per pound of wood.
This is actually an interesting presentation. It does not say 15,000 BTU's per pound.
On page 3, it says 8600 BTU's/pound for hardwoods and 9000 BTU's/pound for softwood. Bituminous coal is 10-14,000 BTUs. Page 11 lists the conditions for good wood combustion. These conditions are the goal of the j-tube combustion system.
For the record, 100% combustion is only possible when using pure oxygen, not the ~19% oxygen atmosphere we are breathing. The upper limit is probably about 95%.
On the Dragon Heaters website, for our "what you can expect" calculations, we used 5,600 - 6,000 BTU/pound of wood. During the intense part of the burn, we recorded 85% to 93% combustion efficiency with Peter van den Berg's j-tube design. These efficiency numbers were logged by a Testo gas analyzer.
It requires vastly different combustion conditions to burn wood than gas. Gas (Propane & Natural) is relatively easy and can be done with a metal jet. The people building metal rocket stoves don't understand or don't want to. They are probably also desperate to lower their fuel bill.
If you want to go vertical, consider bells. Also, heat rises, so its much easier to heat the second floor.
Our designs utilize clay chimney flue liners rather than cob because we are using bells and chimney flue liners are designed to support their own weight. In order to create a cob shape of the same height, you would have to create an very large pile at the base. Clay chimney flue liners can't handle temperature changes greater than 50° per hour, so they have to be insulated by ceramic fiber blanket, dense fireclay bricks, or an inside layer of smaller flue liners.
If I build the battery of bricks and cob on one side of it, would the wall itself function as a thermal battery to radiate in the other room?
Of what is the wall made? Standard frame construction does not a good thermal battery make.
The blog in my signature has an article explaining the difference between bells & flues.
The book does not cover horizontal risers. To me, the whole concept doesn't make sense; by definition, a riser should go up. I don't understand how the heater in the video you presented works. I don't know how well it tests out as far as efficiency. I don't see how the wood is loaded. Consequently, I can't help you imitate it.
We tested a system where the exhaust went up into a steel drum and then it was supposed to go into a chamber under the burn tunnel. It didn't draft properly and we had to tear it down. It was a smoky mess.
If you want to understand about bells, we have an explanation at our blog site. Basically, bells are chambers where the exhaust has space and time to stratify by temperature. The hottest gasses remain at the top of the bell. The cooler ones sink out and flow into the next bell.
One of the things that makes this work really well is that ~80% of the exhaust is Nitrogen which was never involved in the combustion and, consequently, isn't as warm. It goes out faster and leaves the heated gases to conduct their heat to the inside surface of the bell.
Our bell-based designs draft really well and don't need a steel drum.
A bell is not the same design as a contraflow flue.
Be sure to insulate your wood floor from the heat of the burn tunnel. If possible, leave an passage for air between the floor and the burn tunnel. The spontaneous ignition temperature of wood can be lowered by exposure to heat.
it still seems to me that 6 sticks burning would give off more heat than 4 sticks burning
Yes, they will create more BTU's of heat, but we thought your original question was whether they would burn at a higher temperature. This is a factor of the combustion temperature of wood, which doesn't change much depending on how much wood you are burning.
When you use a metal Feed tube -as the entire RMH comes up to temperature- its metal will act as a heat sink and turn into a second chimney, and Bobs your Uncle, back to smoke inside your structure !
This does not happen with Peter van den Berg's design which includes the P-channel which both heats up the secondary air and cools down the metal feed tube.
