April Wickes

Those are beautiful, Pablo. Thanks for the info and warning. Have you found any way to patch cracks?

Pablo, that is a good and important question. I will not be able to answer it until January. However, I did make sure the plaster was reinforced with 2 layers of fiberglass mesh.

And a last summary of the most important design parameters I learned along the way:
Here is the scaleable spreadsheet for DSR3 core dimensions. Don’t try to change the public copy on Docs there, but make your own copy to play with.
https://docs.google.com/spreadsheets/d/1kG219Qu3fmGGtTDFo4IfJOhCPk1RR8Z8/edit?usp=sharing&ouid=114630257550685626397&rtpof=true&sd=true

This was a 5.5” system (the number at which the firebricks and afterburner all came out nice and even). 5.5 is thought of as the diameter of a cross-sectional circle, which means the System CSA (Cross-Sectional Area, your all-important number for calculating proportional dimensions) is pi x r^2, or about 24 in2.

Chimney can be any regular chimney with good draw (ideally insulated). It must be System CSA or slightly larger, so this is often the starting point. I’m getting away with a 5.5” system on a 6” chimney, but you probably could not run a 6.5” system on a 6” chimney! People with bigger houses in the North often seem to like 8”, which (pi x r^2) is nearly twice as large. If your chimney is square, the gas is not traveling in the corners much, so pretend it’s a circle of equal diameter when calculating CSA.

Core proportions matter so get as close as reasonable. Your afterburner tube needs to be able to handle at least 1200*F.

Once you have your core, you then put it inside any heat harvesting bell of equal to or less than the recommended ISA for your system size. Your bell design should have no channels tighter than 5 times System CSA -- and that is for one-way flow. Right above the core, where the gases first expand and swirl around, up, down, and sideways, it is better to have 10 times System CSA or even more.

Do support your floor! Even a little heater like mine is probably 4000 lbs!
Masonry heater standards: Double-walled brick takes an awfully long time for the heat to soak through, so bear that in mind with smaller stoves. Double wall should be built with an expansion joint between to stop propagating cracks. (You can use scraps of cardboard; it’ll burn out.) It needs a minimum 4” air gap from combustibles. Single wall should have more. Single wall should also have reinforced plaster to minimize gases escaping through brick cracks. If hot brick is anywhere in direct contact with wood, I believe code says it should be 12” thick. The front of your firebox and any radiative metal surfaces should have the usual 36”.

Finally you run the exit gases out the bottom and into the chimney. Make sure your exit slot is at least 1 CSA, as low in the bell as possible, and ideally wider than tall, because of gas flow behavior. More is better; you don’t want a restriction there. Do make a cleanout of some kind. In my case I plan to once a year remove the section of black single-wall pipe and snake the tube of a vacuum cleaner down into the exit slot, and also brush out the chimney. Hope that works.

Remember you might need to tweak to your mass by adding extra room to the top box, especially if you couldn’t source one of those sleek and slender ceramic foundry tube afterburners, so design accordingly!

Think that’s all anyone needs to know, right? Happy building!

So long as I am putting all the plans in one place, I should also describe the airframe door. Like the core, this is Peter VanDenBerg’s design, and unlike the DSR2, the outlet vents should be located at the top and upper sides. The air comes in at the front, travels through hollow tubing, pre-heating as it runs, and goes out slots at the top and upper sides, behind the closed door. It then flows along the upper walls of the firebox and ceiling shelf and concentrates right around the port into the afterburner. No secondary air is required.

People who know what they are talking about go on about “laminar flow” with this design but me, I’m just following directions! Earlier testing did show that although a vortex may form when this core is run without any door, you’re definitely going to get some smokeback. So if this is in your house, put a door on it!

Airframe dimensions:
*Bottom member custom welded of flat stock, 2.5” deep by 4.25” tall by 16” wide (exterior dimensions). Interior dimensions are 2x4, or 30% CSA
*Sides are 2.5” square stock, exterior, a bit more than 2x2 interior. 15% CSA each (15 + 15 = 30% CSA)
*Total outside height 13.5” x 16”. Open door measures 7” high x 11” wide. You could increase the height by 2” if you had designed your brick platform to sit the whole door frame down correspondingly, but I didn’t. Oh well. Small door.
*Air inlet centrally located on bottom member, 1.75” high x 7” wide. 50% CSA
*2 Side outlet slots 0.75” x 5”, located high.
*2 Top outlet slots 0.75” x 4”. Add these 4 slots together for 50% CSA as air outlets.
*Air inlet closure is just a piece of flat stock with magnets. In theory, closing snugly at this point will keep the heat inside the bell without an after damper (known to cause CO problems in the house when misused). Leave it open when the stove is not in use, though, and your mild household air will likely circulate right through the bell and up the chimney, cooling the brick and pretty well defeating the purpose.

An important note for those more accustomed to box stoves: While the fire is burning, you are NOT supposed to fool with the air vent. Leave it wide open. You want a quick, clean, super-hot fire; this is why you go to such hassle to source an afterburner of refractory material! You can close it once you're down to a bed of coals.

Once you have the airframe, you attach any door you can make close tightly. I used a cast iron griddle, which my handy neighbor drilled through to bolt on hinges and latch of his own design. (Cast cannot be welded.) Seems pretty snug but if I notice too much air leakage I may later add gasket rope. Any hardware store should carry this, along with the appropriate adhesive. Or at least, any hardware store in Vermont.

It does help, I think, that since Vermont has such a lively sugaring (maple syrup) industry, building supply stores with a good masonry department often do carry refractory materials for the care and repair of evaporator arches. Not sure that would be true in other parts of the country. Shout out to WW in Newfane! Otherwise source parts from pottery supply or discontinued kilns.

Airframe pic taken lying on the floor looking up inside.

Thank you, everyone! It has been a long job. Appreciate all your help and patience.

Scott, I think you are asking about the oven? (I have been using the term “top box” to refer to the chamber housing the afterburner.) So far I have only run single batch fires in a cold stove, and the oven has only reached 150*F. Yes, the mass isn’t getting very warm yet either. However, it is a very small firebox, and a lot of brick! I would say that my ISA (Internal Surface Area for heat harvesting) is probably near the maximum of what a core this size can power. Others have calculated this as about 33 ft2 (200 times CSA). So one batch fire at a time doesn’t count!

Once the weather turns, I expect I will burn several batches in a row to bring the bricks up to temp, and then burn two or three or four times a day to maintain them there. We’ll have to see how exactly that works when heating season starts!

I built a “white oven” (isolated from direct contact with smoke) because there are ceramic fiber products in the smoke path and these are not food safe. I *hope* the oven will get hot enough to bake bread – 400*F for an hour. I hope it won’t get all too much hotter than that because I question the durability of the flue liner, but so far not an issue. I located it high in the bell so it would be warmer, but that may mean that the bell has narrowed too much and the sides of the oven won’t have enough exposure to circulating smoke. Guess if I were doing it again I might go one brick layer down with it. We will have to see. I’ll let you know in January.

Here is the tiny firebox, and all the wood included in one batch. You can see why it would take a few rounds to heat 4000 lbs of cold mass! Firebox dimensions are 11” wide, 9” high, and 14” deep, plus another couple inches depth from the airframe.

Painted. The mosaic came out a little more garish than I had hoped. My friend Allison (who helped with the wall last year) came out again for this, but neither of us had much mosaic experience, so we were just about getting it right by the time we were done.

If I were doing mosaic again, I would:
*Take the time to find crockery of more subtle colors at yard sales first.
*Vary the depth of the mortar bed to bring tiles of different thickness closer to an even surface.
*Be more careful to leave the mortar joints low and empty to be filled with grout! You don’t want the thinset coming anywhere near flush with the surface; the grout is much easier to apply smooth over such irregular fissures.
*Take more time, during the initial layout, to define the edges of colorblocks with the edges of the crockery. Anyway. Here it is.

Luckily I then had a plaster layer to make it all look less lopsided!

Closing it off!

Glass window slot fronted with ordinary cement fiber board, as one would back a tile project with, mortared and plastered into place with mesh. We’ll have to see how that holds. Glass sealed with a gasket rope expansion joint all round.

Oven set. You can see it doesn’t really get enough circulation space. No wonder it runs too cool so far.

Cantilevering in the supports for the oven