Emergency quick and small batchbox for the 400 sq ft wofati (0.7)

If you are into backbreaking labor, you may want to consider isolating the entire slab of heated floor (not the whole floor) with a thick layer of vermiculite (or perlite, expanded clay or shale, etc.). Shouldn't be much worse than double-digging a garden, except you will be making awkwardly large piles of dirt before filling in.

Rick Edwards wrote:

Matt, You said.

Insulating all around the flue would go a long way towards alleviating most of my concern, which is that the giant heat sink of the ground around three sides of the flue is going to keep that flue too cool to work well.

Did you mean insulating the whole mass run but only the bottom and the sides?
I'm assuming not the vertical exposed chimney section, Correct?

Yes, that is what I meant about the insulation. If the flue is in the floor, try your best to decouple it from the ground.

Rick Edwards wrote:The exhaust from the barrel entering the mass incorporates a smoother quicker "Boomerang" transition from its lowest point to a level of 1' covered before it makes the first turn from lateral to lineal.
Roughly 25' will be level before the gentle slope up to the stack from the last direction change.
The Stack has been moved closer to the post.
Questions:
Will the mostly level run help alleviate the condensation problem from returning to the stove?

Yes, most of the condensation will stay in the level part where it is getting more time to vaporize again.

Two points of criticism: Why using that convoluted boomerang to go 2.5' down under the beams when it's quite easy to go over it? In case it's because of the kids one could fence it off with one thing or the other. This would solve the problem of an unknown effect on the barrel and the bare pipe coming out of the barrel.

Second: How are you going to clean the pipe in the floor? There's no side access possible like in a bench. Top access is not favourable due to the drag which is caused by a dead end. Nevertheless, I fail to see other possibilities.

I'd second Matt's point about insulating the horizontal duct from the soil under and at the sides of it.

Breaking ground today. 11/19.

Here's the version 3 plans.

Next 3 views

last picture

And New Version 3 plans download

OK then, the trench is shorter now, give or take 26 ft. I'd calculate the horizontal duct as 39.6 sq ft of masonry, not counting the bottom quarter of the duct. The barrel represents 18.8 sq ft of bare steel, equivalent to 21.9 sq ft of masonry (or cob of course). Together this will add up to 61.5 sq ft so there's about 3 sq ft to spare now.
I still do think the boomerang downstream of the barrel is an unknown factor but probably that would fit within the allowance.

The text in the drawing says under the duct 1" of cob and the trench filled with cob. I hope that's a good decision but only time will tell.

Also, there are several clean-out ports and the part of the horizontal that's closest to the post is above the floor now.

This should do it, don't forget to heat up the chimney before lighting first fire.

Peter : You mentioned something about all vertical clean outs being a drag on the draft, while this makes sense, I have never considered it !

So is there a truly larger effect Vertical over Horizontal ?!

As a corollary, after your system is up and running -would it be possible to have a Plug in Stove Pipe Bell that could be dropped into the top

of a vertical clean out? ( This would seem to require a secondary by-pass damper, and a working plan but as a ''portable/removeable Radiator ''

It seems like it could have value ! (and handles !)

For the good of the craft ! Big AL

Peter,

Rick and I have gone back and forth on the idea of putting insulation under the duct. Rick was very good to point out that you and Matt agree that there should be something a bit more insulative underneath. Perhaps even something as simple as sand.

My counter to that is that for the bottom 20% of the duct, it will be carrying less than 1% of the heat (with more than 80% of the heat riding along the top 20%). Further - I think adding structural integrity to the duct has some value - and fully surrounding the duct with cob will give us that. Further still - I am concerned about condensing water and leaks from the duct - a full cob sleeve should help with that too.

And, finally, since this is in a wofati, and the design of the wofati is to use thermal inertia, then having some heat escape to several feet below the floor of the wofati is embraced as a good thing. We will get most of that back, in time. In fact - I would be tempted to channel the heat even further downward with the idea of putting the excess heat so deep into the ground that it would take weeks to get it back.

So, you make a very good point about heat losses through the bottom. And .... as is the case with nearly everything in the world ... there are many more factors at play. In the end, I made the call.

I wanted to make this clear because I don't want you to think that Rick (or I) is (are) ignoring your excellent advice. Or Matt's!

Paul,

Thanks for the clear explanation.
Like I said, time will tell whether this is the right method. I see the merit of your reasoning and I'm glad you took the time to explain this to a <grin mode> grey-haired skinny pensioner with a big mouth at the other side of the Atlantic. </grin mode>
I am writing here in hopes to learn more in the process so I'm unabatedly interested and like to hear the results.

But you are right, the bottom of the duct will absorb a tiny part of the transported heat. That's why I leave 25% of the duct's internal area out of the calculation. As it is now, the thing should work. Whether or not one barrel is enough to provide direct heat I don't have the foggiest idea because I am in the luxury of living in a moderate sea climate with only a few weeks of freezing a year. And sometimes not at all, the weather deities are whimsical.

allen lumley wrote:Peter : You mentioned something about all vertical clean outs being a drag on the draft, while this makes sense, I have never considered it !
So is there a truly larger effect Vertical over Horizontal ?!
As a corollary, after your system is up and running -would it be possible to have a Plug in Stove Pipe Bell that could be dropped into the top of a vertical clean out? ( This would seem to require a secondary by-pass damper, and a working plan but as a ''portable/removeable Radiator ''
It seems like it could have value ! (and handles !)

Al,
Yes, in my opinion the drag is larger on top because the majority of the hot streaming gases are at the top of the duct. The bottom is the best place for a clean-out then, but in most circumstances not very practical. A good alternative would be a 45 degrees down placement.

That plug in bell is an old idea and tried out by the Masonry Heater Association as far as I know. It does work admirably well, a barrel with a hole at the bottom could be placed over a vertical clean-out and this will warm up without a hitch. This could be done on the fly while the heater is running, but also as a more permanent instalment with a simple sliding valve which is opened after the heater is getting up to temperature. A stove pipe bell won't work that good because the ratio of pipe vs bell cross section area should be 1 to 4 at least in order to allow stratification.

This bell idea could be implemented in larger systems which need a lot of heat for the chimney to start up at all. Now I come to think about it, it's already done by someone who placed a 55 gallon barrel at the end of a short bench.

So we are casting a 6" octagonal riser using Matt's ghetto casting tech. Using the 14" diameter grease drum as our outer form for the bottom three fifths and a sheet of galvanized metal for the top two fifths. The inner form is wooden and will be burned out. The inner octagon is made from our rough cut 1 x 4s off of our sawmill. Then I ripped them down with a circular saw set to 22 1/2 degrees on both sides. Didn't have access to a table saw but here is a method to not let that stop you. The sides of the octagon pieces needed to be just under 2 1/2" on the long side for 6" across the mold. The first pass on all eight boards was done to 3" wide, following the straightest side. The pictures below show the first pass on all boards.

The next pass on the eight boards. To do this, I took a piece of the offcut 22 1/2 degree ripped first cut and screwed it to the saw guide. Set for 2 1/2" wide and rip them down a second time.

More pics of second rip on boards.

Now to assemble the boards. We had large hoser clamps leftover from the 0.8 RMH workshop for the clamping. If these weren't around, this could have been done with string or rope. Once the clamps started cinching just a little, the boards mostly adjusted themselves into perfect position. A tiny bit of encouragement on a couple of boards to get all outer edges flush and voila! A proper Captain Kirk cannon.

Phase two of assembly. Each board received 3 screws; top, middle and bottom. Using a trim head screw, they buried down under flush. All holes were pre-drilled with a 1/8" bit so the boards wouldn't split apart. Then remove hose clamps.

Very nice!
I know how to do this, but I am a wood worker by trade and and did some years as a model maker as well. I did this once before, using a table saw. It is definitely quite some work but worth the effort and not as complicated and time consuming as a round inner mold. Posting the process as an illustrated feuilleton looks like a how-to-build-a-batch-box course.

Please, go on!

I am probably crazy, but this whole adventure is the highest drama!! ;) I am 'glued to my seat' !

Deviation on octagon is from 6 1/32 to 6 5/32. So +/- 1/16". Plenty good enough I think. And again, easy enough to do without a table saw if need be.

Last picture shows the forms put together. I had a sheet of aluminum that I screwed the octagon to. Then set the grease drum in place upside down with the bottom cut out so the sheet metal had a captive lip to sit on. A couple of screws in the sheet metal and we are ready to pour. (More like stuff actually than pour)

Looking good Rick. For removal from the completed riser, will the octagon simply be burned out? I'm wondering if it can't be saved for reuse, maybe by coating it with Paraffin wax or something other to serve as a release agent.

Byron Campbell wrote:I'm wondering if it can't be saved for reuse, maybe by coating it with Paraffin wax or something other to serve as a release agent.

There's only one way to make a rigid mold like this re-usable, by making it conical. I've made one years ago and used a plastic bag around it as a release agent. The thing was cast with refractory concrete and despite the conical shape I had lots of trouble to get it out. So, a straight mold without a release angle doesn't stand a chance to get out apart from destroying it. We moved house 6 months ago and the mold showed up again, keeping it for 20-odd years and ending being dumped in the tip.

Good point Peter.

Probably the easiest method would be to make the octagon two pieces, i.e. split the octagon along its length, maybe even three different splits would be better than two. Then wedge it slightly larger in diameter with foam stuffing, and wrap the whole outer area with thin plastic. Then for removal, simply remove the foam core and collapse the octagon.

I had to look up feuilleton. Contemporary America, it is a story done in installments. Contemporary French, it is a soap opera. I think we qualify as both meanings.

Byron, yes the inner form will be burned, also using Matt's ghetto casting tech, it seems to need to be burned out to hold its shape until fire cures and hardens it.

Matt, if we wanted to do this nicer and maybe shippable, would you use the spar this or that, and with what other ingredients for thinner walls and crack reduction?

Yeah, castable refractory of some flavor, and stainless needles. You guys should have both. I think that cracking is a given, but it would probably hold together as long as it wasn't moved around much. Those ceramic fiber risers are a better choice for those design goals, in my opinion.

I started a new thread "casting tech corner"
https://permies.com/t/41607/rocket-stoves/Casting-tech-corner#325849

So we can discuss any and all casting or shipping tech that people wanna share.

Couple questions.
1. My P-channel is I.D. 1.834 x .834". My plan is to have it extend down .834" below the top of the port. Is this correct?

2. The plans show the port at 9"tall. The formulas give me 9.5" tall. I can notch the two bricks that make the top of the port to give me 9.5". Is this advisable?

As an aside.
Has there been limits found on the port throat depth? With current design, the bricks make the throat 2.5" deep before entering the riser space. I'm not changing this design, but curious if shorter or longer has been tried and with what effects.

The core ready to be fired.

The boomerang and parascope are installed.

Ducting and trenching

Rick, go for the 9.5 i'd say, and make your p channel overhang 11mm( i think that's what Peter said at some point during developpement.) like this you'll be neat th 9" figure originaly drawn

Ready to cut and bend the P-channel.

Rick Edwards wrote:Couple questions.
1. My P-channel is I.D. 1.834 x .834". My plan is to have it extend down .834" below the top of the port. Is this correct?

Because of the slightly different dimensions of the p-channel tube, I would say the overhang could be 0.5".

Rick Edwards wrote:2. The plans show the port at 9" tall. The formulas give me 9.5" tall. I can notch the two bricks that make the top of the port to give me 9.5". Is this advisable?

There's some tolerance in the dimensions. What you can do is check the csa of the port, this should be close to 72% of the riser csa. Minus the overhang of the P-channel should give you something in the region of 68%.

I've done the math for you and in my opinion you would do best to notch the two top bricks and get to 9.5" high.

Rick Edwards wrote:Has there been limits found on the port throat depth? With current design, the bricks make the throat 2.5" deep before entering the riser space. I'm not changing this design, but curious if shorter or longer has been tried and with what effects.

Up to 4" depth of the port I could only find minor differences. Probably because the afterburner flame happened to be further away. Above that, the time to heat up properly became longer and longer. So, no problem as long as the port depth is between 1" and 3" I would say.

Thanks for showing the process, here, people. Even for those of us who are a ways away from making it happen, it helps to visualize and hear the specs so that one day we can do this, as part of a team or alone.
John S
PDX OR

Today has been very busy with project progress. Maybe bunches more steps shown tonight. And thanks for the thanks.

Great thread Rick. I'll be keeping a close eye on this "little" project.

"Just in time" innovation in the spirit of Salatin's "Good enough is perfect". Looking forward to seeing how it all plays out.

So I'm uploading 4 videos right now to YouTube which is keeping my phone from being able to upload pictures as well. So I'll get stuff posted tomorrow a.m.

Jesse, glad your enjoying it. Although now that this little project is permanent, I am taking time to make things a bit closer to as good as possible within reason.

We got the riser fully burned out by setting it on Tim Barker's J-base, in the rain, finishing in heavy snow. Thing was crazy heavy. 14" OD, 6" ID and over 43" tall Is a lot of material, it used almost two full batches of the ghetto tech cast mix. 1 to 1 Lincoln 60 fire clay and perlite, 25lbs furnace cement (~2 gal) and pulled fiberglass bat insulation.

I placed the large outer barrel on top of the riser with 3" standoffs so the outside of the riser would get heat as well as the inside.

The P-channel is done and all fire bricks are cut to size.

Local clay and sand mortar is ready for the red construction bricks. There will be four pillars of 6 of these to hold the barrel above the BatchBox.

Lincoln Fire clay and sand slip mortar is ready for the fire bricks.

Lincoln fire clay and sand mixed to pottery consistency for ramps.

Hole cut out of lid for barrel and will shape to fit riser in the a.m.

Also need to cut and fit hole in barrel side for duct exhaust run

Yeah Rick, this is fun. Great job dude.

Here, the extra metal at the top of the form proved to be an excellent tripod standoff in the making. I love happy accidents as my 7th grade art teacher would say.

Setting the riser on Tim Barker's J-base and covering with a barrel to burn out the inner form, and heat the outside of the riser at the same time.

It was raining so we had to set up a make shift umbrella over the woof feed.

The first load was mostly burning up due to the cold system and the wet riser.

The second load you can see was mostly burning correctly.

We didn't bother priming the system. It would have been a waste. Just had to let it take it's own course.

Checking progress.
Form is pulling away from the riser and charing.
Lots of creosote from the smoldering burn out.
Night shot.

P-channel and brick work.

Some night shots of the the riser being fully burned out.
My beautiful octagon has burned away. Leaving being a beautiful octagon.