Sourcing J-Tube construction materials

I'm interested in building a J-Tube Rocket like the ones that appear to be in use at Wheaton Labs (pictures attached).  The one on the left in the picture heats the shower water, and the one on the right seems to get used frequently for boiling pots of water and cooking rice for PEP BBs.  Both look like very similar designs. One has a longer burn tube and taller heat riser. It looks like the water heater one was later modified to have a taller feed tube and heat riser to reduce sooting.  I have several motivations to build one: a) to learn how to build one by building one from scratch, b) to have one on hand to earn some rocket related BBs, and c) to use to boil Big Leaf Maple sap to make syrup.  Currently I use a combination of a propane crab cooker and my wood stove to make Big Leaf Maple syrup, so it would be nice to replace the propane crab cooker with a J-Tube rocket.  I boil the sap in a stainless steel catering pan that is 13 inches wide by 21 inches long by 6 inches deep (picture attached).  Large quantities I boil outside, smaller quantities I bring inside if the inside humidity is low.  I would likely modify the top of the heat riser to better accommodate the catering pan so that it doesn't just scorch the sugar in the center of the pan.

For some reason, I particularly like the design of the pictured rockets.  I already have angle iron and welding capabilities, but I'm curious to know:
1) do folks familiar with J-Tube designs like this design?  What are the pros/cons?
2) what materials were used (other than the angle iron)
3) what are the actual dimensions of those J-tubes
4) is there someplace online where the materials can be purchased (Amazon?) Has anyone already put together a shopping list with links to where each item can be purchased?
5) which of the two pictured rockets would you recommend for my application - shorter burn tunnel or longer and why? (for boiling sap)

The pictures attached are from the 2019 ATC Thread.  I've searched extensively and haven't found any Permies Forum threads specifically about the construction of these two J-Tube rockets, so if those exist please link me to those threads.

Thanks in advance J-tubers!

Hello R.   Welcome to the world of rocket powered fire!

So much to learn and experiment with but also quite a few proven designs that are out there to get you going.

Matt Walker over at Walker Stoves sells an assortment of plans to make a rocket stove very similar to the pictures you posted.
Luke over at Rocket Stove Cores sells Matts cores pre-made as well.
Made from ceramic fiber board and skinned with aluminium (or other material) to be made portable or surrounded with brick/cob for a permanent installation.

I'll try to answer some of your questions

1 & 2) The J tube is the base design for rocket stove cores and has been proven to work very effectively at burning clean and easy to build from simple inexpensive materials (soft red clay bricks, cob, perlite etc), to high tech modern materials (ceramic fiber board/blanket, insulated firebricks etc.).
If you love fire and can be close by to feed it every half hour or so while processing your sap then it would be an excellent choice.
3) J tubes typically are either built as a 6" or 8" system being the most common. Dimensions are given in the books listed below or on many build threads here on Permies.
4) Materials can be as close as your backyard (for clay and sand) or to your local hardware store/ brick yard that will carry firebricks, fireclay etc. Also, there is a new business run by the rocket mass heater forum leader Thomas Rubino called Dragon Tech.
5) Generally the burn tunnel is kept around 1.5 -2 times the length of the feed tube. Any longer and you may run into problems and is harder to clean.

If you haven't already read the Rocket-Mass-Heater-Builder-Guide  or Rocket Stoves Third Edition than these would be a great addition to what you can glean from the forums here.

Hi R;  Those look like early Matt Walker stoves
He has an aluminum series J tube for sale.
Here is a link to his store. https://walkerstoves.com/index.html

Also Luke is selling Ceramic cores that you assemble.  http://rocketstovecores.com/

I have built two rocket fired maple syrup evaporators, for 8 square feet of pan and six square feet, both powered with L-tube rocket cores. The critical factor for evaporators is maximum and sustained heat production, and the 30" long, 8" wide x 9" high horizontal burn tunnels of my cores (plus 30" tall heat risers) allows a lot of fuel to be burning at once. For your smaller pan, you could use a smaller cross section like 6" x 8".

Here are a couple of threads of good rocket evaporators: Rocket Stove Maple Syrup Evaporator and Maple Syrup Shop Heater Update .

What density of refractory ceramic fiber board should be used?

From reading other posts, it sounds like 2300 or 2600 F rated boards both work fine.

In another thread Thomas lists an EBay item number 222715872389 for the ceramic fiber board but that number isn't found on EBay anymore. If someone knows which board to get on EBay, could you post a link here?

For an evaporator, I would advise the strongest available cf board for the feed and burn tunnel, to resist the large quantities of wood you are going to be putting in. The heat riser can be the softest as it will never see mechanical abrasion, but it will see some of the hottest temperatures at its base. I would actually make the feed, wherever wood is going to touch the sides, from hard firebrick, as that will be most durable. It may take a few more minutes to come up to temperature, but when you are feeding for hours that is irrelevant. Then insulate heavily around the firebrick; ordinary fiberglass or rockwool insulation is fine for that as it will never get hot enough outside the bricks to damage the insulation. Save the expensive and high-grade ceramic fiber for the heat riser.

The closest possibility for local ceramic fiber board I've found so far is about a 2 hour freeway drive one way.  Looking at their many choices of Nutec board specifications, the density options appear to range from 12-46 (192-737) in lb/ft3 (kg/m3).  Continuous temp ranges from 1832-2800 (1000-1482) in F (C).  What have people been using for density?

Glenn,  I am currently using rockwool insulation around my hard firebrick batch box core and it is holding up really well with a season of use. Don't think I would ever use regular fiberglass insulation though anywhere near the core. I think it would just melt, even at the base of the feed in a J tube. Curious to know if you've had experience that proves otherwise?

I haven't used fiberglass (or rockwool) in a J-tube. I have built two L-tube rockets for maple syrup evaporators, and both have fiberglass around the back 2/3 of the burn tunnel and the whole riser. I haven't disassembled them for inspection, but peeking shows that the fiberglass is still around the risers where I can see. The second one had to be thrown together with insufficient brick at the top of the riser, and there is still fiberglass in the gaps. I think some of the fiberglass melted near the inner face of the riser. These 8" x 9" cores were run full blast for as much as 10 hours at a time, so have had their trial by fire.

So here is what I've found so far for sourcing refractory ceramic fiber board for the build:

The company is Distribution International.  They have a few branches throughout the USA, one within about a 2-hour one-way drive from me.  The ceramic fiber board they carry in stock is part number CFBD1034N and is 1" X 36" X 48" CERAMIC BOARD by NUTEC.  It is $95.45/board plus sales tax.

Here is the description from the manufacturer:

MaxBoard®LD-2300
MaxBoard LD-2300 insulating board is a low-density product
manufactured to tight dimensional tolerances and an excellent
surface finish. Considered for application in appliances and
equipment where aesthetics, uniformity and performance is
important. Its temperature rating up to 2300 °F makes it an
excellent option for a vast range of applications.

Below are the specs.  Do you think this will work and last a long time, or should I ask them to order in some of one of the other non-stocked models with higher density and higher temperature rated specs?  Or should I keep shopping around for a different brand and/or supplier?