April Wickes

Hi Mattias, thanks for checking in.
I’m pretty sure this didn’t work as a DSR3 because of the experimental parts I had to fudge. That’s not a problem with the design of the DSR3 – but it does seem to mean that if one cannot actually follow that design, one had better be prepared to do some troubleshooting. Square afterburners may behave differently.
As a Vortex core, it is now working reasonably well, although not nearly so fine and steady as Fox Martyn has achieved. It smokes some. Some days I can only get a fire fountain, not a vortex. Seems to depend a lot on the weather and wind.

We are still in heating season here so I will post an update when I do the spring cleanout. I will assess how much creosote buildup there is then.

What you are seeing in the door is a bit of an optical illusion. What it is, is that the door sits high on a brick platform with no room to extend below the firebox as many of the airframes do. So the bottom member of the airframe is covering the front of the lower part of the firebox. The air exit slots to feed the fire are as high as they could go while maintaining Peter’s proportions, and are indeed in the upper half of the firebox. However, since switching to the Vortex core, I wonder if it might not be happier with a little lower air.

The ISA of the bell is about 33 ft2 (roughly 3.3 m2). This was calculated as reasonable for a system of this size, but maybe would be better with a radiating bell such as steel. As brick and cob (about 6” thick on the dome, 8-9” on the lower box), I feel like I have to pour a lot of heat into it to get much back out, so the core may be undersized to power it. Also, when it is below 0*F with a 50+ mph wind, I have to keep the stove running continuously all day and my house is still chilly. (It’s fine under any more moderate conditions.) So perhaps I should have built a slightly larger core.

No, no bypass, although I do have a priming hole in the chimney. I have not needed it. It lights and draws just fine.

Thermal cracking in the brickwork has held steady in the same places and to the same degree as when it first appeared. I’m mostly not worried about it. Carbon monoxide alarm has remained silent all winter, so it can’t be leaking much.

Glad to hear yours is working well for you!

Hi Tom and Linda,
Well, there's me, but I'm closer to Brattleboro, so as they say, you can't get there from here.
https://permies.com/t/266494/DSR-Beehive-Dome-Completed
I do seem to have done it the hard way but I'm generally content. Pick a simpler rocket core and a square brick mass, your life will likely be easier.

What I like:
* the house is still 55*F on -10* mornings, even though I'm sleeping through the night. With the box stove, if I didn't get up at midnight to feed it, there was sometimes ice on the toilet by dawn.
* I am indeed burning less wood, probably about 1/4-1/3.
* It does seem to be less smoky overall. Jury is still out on creosote buildup. I will have to update when I do the spring chimney clean.

What I don't like:
* I can no longer just stuff the thing full, choke it down, and head to work. I also can't leave it wide open to finish its burn without losing all my warm house air up the chimney afterward. So I need to spend a fair amount of time at home tending the fire.
* I think my core is bit undersized, both for the house and for the brick bell. So I have to keep it firing more or less continuously on very cold days and it takes a lot longer to warm the chilly house than the box stove did.
* Still haven't found the right setting for a truly stable burn in the Vortex core. That makes some messy smoke. Other rocket cores are likely to be less fussy.

If you want to discuss it in more depth, you can PM me your phone number and I'll call.
Thanks,
April

Well in this case, it was a case of *could* not follow the DSR3; I couldn’t source the right part.
As for the Vortex, I’ve felt a good bit of frustration figuring out exactly what the design IS, and I suspect I am not alone in that. That design has changed over and over and over again along the course of the (extremely long) development thread! Put a stumbling block in, nope, take it out entirely and make a shallower top box, nope, put it back in ….

This particular balance of chimney draft (strong, by the way), expansive bell, and high-located air intake seems to like having a stumbling block. It likes it a lot. Two burns in a row with the present configuration have behaved quite well now, even though today is muggy and windless. If it keeps up like this through some windy storms too, I will be content.

So, presently working Vortex configuration on this 5.5” system (23.9 in2 CSA):
* 20% primary air, no secondary. Because I have an airframe, this is delivered high in the firebox rather than low; I might look into whether lower-located air improves the slow coaling at some future date. Needed the door cracked open to catch the kindling alight, but then let it develop slowly. Fire remained well controlled throughout the burn.
* Firebox and port as is. Shelf between is extra thick because I wanted to raise the short vortex into the center of the round viewing window. It doesn’t seem to make any difference.
* Afterburner 4.2” high, 8” wide, more like 12.5” deep (my glass window is plenty sheltered behind the thick front wall; if yours isn’t, you should leave the full 4” gap.) Insulating material of course! CFB scraps at the moment. I will probably try to rebuild with something less toxic where possible, or at least coat it with sealant.
* ½” stumbling block restriction as it passes into the upper shelf chamber, plus a couple of scraps to narrow the full shelf width. So that’s about 1.7” x 9” or 65% CSA – a little bigger than recommended (in the mid-thread range of Vortex designs at least) but I don’t think I’d want to slow this fire down any more. Trev was calling this an “exit port,” meaning the exit from the afterburner, not from the whole core. This was placed back about ¾” from the shelf edge, as recommended.
* Upper shelf chamber 2.2”x 11”, or pretty near 100% CSA
* Final exit into bell 2.4”x 8” or 80% CSA.

A surprising note: Over the last few days of harried testing, I needed some ½” spacers in odd places, like between layers of the shelf and to temporarily replace the cooktop and form the stumbling block. I had some scraps of ordinary cement board leftover from a tile project, I think HardiBacker brand [?]. Dense cement and fiberglass integral to the mix, tough to cut. I threw it in because it was the right size, fully expecting it to burn out immediately. It didn’t. It appears completely unaffected. Wouldn’t trust it structurally in a refractory setting but I’m impressed. The stuff is certainly cheap enough to experiment with!

Video is a limitation in rural Vermont, so that likely won’t be coming. Fox, I will try to make a day to go sit in the public library with headphones and watch more of your videos … but that’s what it takes with our shonky internet here! Thank you for your fantastic public service in creating them. I look forward to it.

Better. I temporarily blocked off the raised cooktop to make an even ceiling across the top box. I narrowed the shelf slot above the afterburner to somewhere between 100% and 110% CSA (not such precise materials as Fox’s fine glass!). And I found some metal scraps and magnets to block the primary air down to 20%. The airframe as designed let in a LOT more primary air than that, more like 50%. This may have been a good bit of the problem. So I am now a lot closer to the recommended Vortex proportions.

I am definitely not getting such perfection as Fox shows in his video above. Start up was again a sooty mess, but it was closer to 15 minutes than yesterday’s full hour of guck. After that it ran acceptably. Today the vortex lost its oomph faster than it should have and overfueled some on the reload, although not terribly.

Sure wish there was some step by step plan for troubleshooting these: If this, try this; If that, try the other. Fox’s results shown above are indeed fantastic, really breathtaking … but those four+ years of fiddling are exactly why I didn’t just build a Vortex core in the first place! Still, we’re on the right track.

Thank you, Fox. Got links?

So: that expensive ceramic fiber glue from Ceramaterials may be fit for some purpose, but obviously not this one. It burned right out. I no longer have an afterburner tube. Yes, I could probably try holding the pieces together with some sort of stainless steel band, but at this point, it seemed I should cut my losses and rebuild the afterburner as a Vortex, which can be made of much more easily sourced – rectangular! – pieces.

This meant:
*Vortex firebox can be a bit taller but essentially the same, so no changes.
*Kiln shelf between firebox and afterburner, with its port, is identical.
*I restricted the final exit from the core into the bell with a chunk of brick so that it is 80% System CSA (2.4” x 8” on this 5.5” system) instead of the full width slot of the DSR3.
*I removed the wrecked tube and built a different afterburner with scraps of CFB. It is 4.2” high and 8.5” wide (150% CSA and proportions matter). A shelf covers the top, 12” deep (4” from the front wall and glass window).
*Just like the DSR3, the gases combust in the afterburner, pass forward toward the viewing window and then turn 180* back. They pass over the afterburner shelf through a wide shallow slot – which should come out to roughly 100% CSA; mine is a bit too big at present, given the scraps I had to hand – and then go out the final exit (80% CSA).
*In my case, since the front half of my upper box is 1” taller than the back half, I added a 1” stumbling block to slow the gases down through there.

Later, I may try taking that extra height addition right off and lowering the cooktop back to my original design (9.5” top box height all the way), but for today, this is good enough. One disaster at a time please!

Initial firing as a Vortex core burned okay – good draw, fairly lively activity in the afterburner, a little sluggish but certainly not overfueling. Second firing did overfuel messily for about the first hour and then, by a judicious fiddling of extra fresh wood and restricted air, I was finally able to bring it to a good burn. Reloads thereafter were fine. So I’m still having the same pattern of problems as I did with the previous configuration.

I know the Vortex design likes to be “tuned to its mass,” which is to say I may be futzing with it for a while until I find exactly the right balance between exit resistance, air intake, and chimney draw. Anyone knows more about troubleshooting these, I’m listening.

Is the kind of weak vortex seen in the picture below what you get when there is too LITTLE restriction in the core? Counterintuitive but maybe?

And picture of a reasonable burn … eventually.

UPDATE 12/6/24:
Well, the news is mixed. The stove continued to behave erratically, working well about 2/3 of the time, overfueling sootily about a third of the time, and occasionally bolting into a rather terrifying runaway. This behavior was frustratingly unpredictable and seemed to depend on tiny variations in the stacking of the fuel load, or maybe just the weather. I never found a clear correlation.

My conclusion is that the octagon made of 1” wide materials (rather than the round, thin-walled foundry tube that the design calls for but I just could not source), simply did not provide the same restriction in the gas path and stabilization of the burn that the DSR3 proper is supposed to provide. Because my afterburner was a different shape than Peter’s exact design, in order to achieve a good draw and prevent smokeback, I had to add too much extra room in the top box and this made it prone to overfuel. Nevertheless, it was heating my home reasonably well, and I was enjoying the house being less frigid in the mornings, as a good brick bell offers.

Then, barely two months into use, this happened:

All right, two week update.

My biggest problem is this: The burn is not stable.

It consistently draws well. It is usually not difficult to light. I am doing top-lit fires with dry wood, mostly red maple and ash. So that’s a couple of big pieces on the bottom, a couple medium on the sides, and (since the firebox is so small) a hollow V of kindling in the middle (birch bark, a twist of paper, pine or maple splinters). I try to make sure all logs have a bit of air between them.

Some days it burns fantastically, start to finish, just as designed.

Some – most – days it stalls out. The afterburner flame goes dull red and sooty, and the door must be cracked by ¾” to get any vortex at all. It does not smoke back. I can still feel the draw whooshing by my hand. Sometimes adding lots of exta air around the door will return it to a reasonable burn. Sometimes I can fix it by adjusting the logs in the load, moving one closer to the center after the center burns out. Often it seems a one-stick reload corrects the problem and then it all burns merrily until reasonably well consumed.

Occasionally – and so far as I know I have changed nothing! – it takes off with a roar and comes gushing out the front of the afterburner to bounce off the glass. I have been trying to correct this by restricting the air some. I am not sure if that is the best way to deal with it. Seems like Trevor’s Vortex advised actually the opposite??

Today is one of those, overexcited at start up. About 30 minutes into the burn, it settled down and started burbling along contentedly at the back of the CFB afterburner, which was glowing dull red. It is presently running with the recommended air, but now, about an hour into the burn, it’s slowing and I’m wondering if it needs more air again. No soot, anyway. For once.

So what’s up? Is it that picky about exactly how it is loaded? Is it that sensitive to exterior weather changing the chimney draw? It’s seeming finicky, all round. Would definitely appreciate advice!!

Other updates:
Yes, Pablo, I’m getting cracks. I don’t know whether or not they are serious. There are none in the main dome yet. They’re mostly at places where one type of material meets another, so, bottom edge of dome where it sits on the square of double-thick common brick; around the firebox where insulation meets the brick; in front of the glass where I cobbled together a holding slot out of ordinary cement board and plaster (I am not at all surprised that moves!) They are visible during the burn and close back to invisibility after it cools. I do worry about the lintel, but otherwise, I think the only real risk is carbon monoxide. (Which could possibly leak around the cooktop too.) I have bought a CO meter and set it next to the couch. So far it’s not whining at me, which is good. Unfortunately it isn’t a constant meter, but will only display the CO reading when something is wrong.

Chimney temp still 120*F.
House air temp today raised only 2*F during the 2 hr burn, although radiant near the front of the stove was plenty. +2* more over the next 2 hrs, +4* over the following 2 hours, and probably will continue to rising for a few hours yet. There remains some sense of heat, perhaps a bit nebulous, about 12 hrs on. Enough to turn your head as you walk by, wonder where that’s coming from.

Back of the oven after one load + one stick for 2 hours is 200*F. Not enough to do much with beyond a slow roast or drying something. Still hasn’t been cold enough to keep the stove running for more than that per day. Winter Is Coming and all, but so far just light frosts.

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.