Peter van den Berg

I'll try to answer your questions to the best of my knowledge.

To my eye, what's visible from the chimney top appears to be water vapor. The heater is only 4 days operational now, so it isn't in full working order yet. Lots of water is used for the build and that needs to vaporize and exhausted as vapor out of the chimney. On top of that, the process of wood burning, on a chemical level, is producing heat, CO² and... water. The exhaust gasses' temperature is quite low, so water vapor will condense as soon as it comes out in the air. Within a few yards it should disappear from view, unlike smoke that can be drifting visibly away for a mile or more.

So that white smoke isn't smoke. Try to have a sniff at it, when it smells like wet charcoal combustion is very close to complete already. That smell is from 9-methyl-ethyl-ketone, one of the last large carbon molecules that is being cracked.

A freshly built heater will smell like drying cement which in fact is what happens. Once dry, the whole of the system will operate in underpressure and the smell will disappear. Whether or not there are other smallish leaks is hard to diagnose at this distance. A dry stove doesn't extract any heat from the fire in order to vaporize water, so within a month you'll see that you need less fuel as compared with the first days/weeks.

The ash situation is such that there is unburnable content in woody fuel, the minerals that the tree extracted from the soil. So there will be ash leftover, no escaping from that. Just scoup somewhat out now and then and leave a layer of ash on top of the floor channel at all times.

I never said fuel consumption would be 1/10 of any steel box stove. Maybe as compared to the absolutely worse pot-belly one, see it as a sort of urban legend. Cutting your fuel consumption in half is already quite a feat, it might even get better in time.

A question or two: why is there a a smaller piece of stove pipe, right under the ceiling connection? In case this is smaller than the required 8", please replace that with the right diameter pipe. I can't see the chimney top in the first picture, just the plume. Is it elevated at least 2' from the top ridge of the roof? In case it isn't, I'd recommend lengthen it with a double walled and insulated chimney pipe.

Please keep running the heater daily, you are on the right track.

Mike Haasl wrote:And the sides of the U also help hold things together?  Probably so it's more moveable?  If you were building this in one spot and never going to move it, would you need sides on the U?

Yes.
That's one of the possibilities, yes.
Yes, definitely, so it all stays in one piece while it is in use.

When you say "the bricks are sticking out one inch", that would be in the middle of the firebox. Left and right, it would stick out two or three inches. For a 6" system, the core would stick out a lot more.

Mike Haasl wrote: Looking at the Batchrocket.eu designs, if you wanted an open system without a door, couldn't the bricks just stick out like on Peter's older shop heater?  Then you can skip the welded box on the front all together?

What you see in the picture is a cast core, supported by a brick column at the inside and one outside the barrels. The column inside is resting directly on the floor, so there's a slightly larger opening in the barrel's floor and the opening between steel and brick stuffed with superwool. Around the cast core and the steel of the barrel there's another stuffed gap. Both these seals aren't really permanent, the steel moves quite a bit with heating and cooling so regular (montly or so) inspection and maintenance is required. Despite being a barrel heater, it won't be movable at all, not even a tenth of an inch.

The one with the steel box inside will remain movable due to its construction. No rigid connection to the floor, the interface between box and barrel is welded or riveted, all steel is separated by a layer of superwool from the firebricks. There's no brick column inside the barrel so there's less mass to heat up. Most of the downsides of the old one are eliminated in the  construction of the newer shop heater.
All in my own opinion of course.

Mike Haasl wrote:First off, from your pics above, I didn't realize the steel box went into the barrel, I thought it just stuck out :)   Does it continue all the way across the barrel to provide some connection at the far end of the barrel?  If so, I'm wondering if there's enough CSA on either side of the U tray to let cooling gasses get past the firebox and down to the exit?

Yes, the u-box continues across the inside of the barrel and is tack welded to the rear wall. That's how all of the core is supported, the structure is the steel box. Bricks right against the inside of the box won't work, there won't be any play room in there. The superwool can be compressed a bit so there isn't a rigid wall around the core. At the place where the riser is, the wool is applied in a double layer left and right.

Yes, there is enough csa on either side, the gasses can past there easily and slows down again under the core. In fact, the space there act as a manifold, a very spacious one with that. Fine dust will settle at the barrel's floor, the riser is close to the barrel's wall which means the front of the barrel will warm up first.

The same sort of construction has been used for a 6" core in a three barrel tower and it worked beautifully. The core sticks out more, full firebricks inside the box but 1/2" superwool around it this time.

Mike Haasl wrote:If I used split firebricks, does it need insulation around the firebox?

Se above, the bricks are allowed to expand and contract thanks to the insulation plus it's a lot easier to assemble the core inside the box.

Mike Haasl wrote:It sounds like that design doesn't have a P channel or any sort of secondary air tube.  It even sounds like the front is only partially covered.  That would make it a lot easier to build...

Exactly what I had in mind while designing this shop heater. No glass, no secondary air channel which means it will act as if it would be an open system. It does need a proper chimney, though.

Mike Haasl wrote:Peter, how did you fit the barrel around the fire brick assembly?  It looks like if it has to extend out into that metal box, you'd have to put the brickwork together inside the box and barrel.

The superwool got in first, then the split firebricks, done with very thin layers of a refractory mortar. This'll work, has been done before with a three barrel tower. The top of the steel core box is mostly open, only closed where the barrel's wall is. So front bricks first and riser last. Because the superwool had a tight fit, everything was supported nicely.

Mike Haasl wrote:When they were finished, how well did they work?

What I've heard about those shop heaters they work quite well. I have to contact the guy who initiated the whole of the workshop. I'll ask for more pictures, possibly there are videos now.
Initially some were used as an open system, others were planned to have a door of some sort. The air supply was done through a smallish frame, vertically mounted steel plate in the middle, blinding the opening for 50%. The rest of the opening a spark screen, left and right of the middle plate. Simple, very efficient and very quick to shed heat.

Mike Haasl wrote:I had a dream last night about a small batch box that fit inside a stack of two 55 gallon drums.  The total footprint of the heater was the drum diameter.  It didn't have hardly any mass so the heat all went right into the room.  This gave a quick, fast heat but it lasted as long as the wood was still in the firebox.  Perfect for a shop or garage that only needs heat for a half a day every once in a while.

Hi Mike, your dream has been materialized before, last November to be precise. I've conducted a workshop building 7 of these double barrel heaters in two days. Most of the work was done although none of the 7 items was completed at the time.
To begin with, these were open-top barrels but the clamps wouldn't fit two top rims. So instead the bottoms were cut out because the bottom rims are thinner and two of those would fit in one clamp together.

What we did next was cutting and folding plate steel in a sort of U-shape. Each U-box was provided with a front that could shield the thickness of a split firebrick plus 1" superwool. A partially lid on the box provided for the barrel connection. The core was entirely made of split firebricks with superwool around it bar the front and the bottom. Height of the box was enough to house the core's height plus a space of 3/4" where the top seal would go. The whole of the core is built into this U-box, superwool along the sides, rear end and top.





The riser will be a 5-minutes item, resting on top of the core. The bottom end of the riser is just square and built out of split firebricks as well.

The interface of the U-box to the barrel is tricky, indeed. But it can be done by means of cutting out a smaller opening, bending and hammering a 1/2" flange around.



The opening can be made a bit wider so the core box slide in easily. By hammering the flanges back a good fit can be established.



This particular core boxes are all spot welded to the barrel, front and back. Of course, this could be done by drilling holes and pop rivet the assembly together.



No pictures af the final product, but I think you can get a clear picture of how it can be done. By the way, this is a 5" core, due to the split bricks it'll fit perfectly. As you can see the whole of the core is in the lower barrel, only the riser will be sticking out. A low mass core, insulated around and a 5 minutes riser to go with it. The top barrel can be disassembled for maintenance, exhaust is about 6" from floor level, wherever around the perimeter of the barrel.

david higos wrote:If I understand correcty the recommendation to lift Aurelio's benches was not a matter of seating comfort but to ensure effective stratification. Is this right?

Yes, that's right. Assuming the top of the bench' seat would be somewhere between 45 and 50 cm, the height of a normal chair, the inside of the bench would be 35 cm high, enough to ensure startification.

david higos wrote:I would like to be sure I understand what Peter means when he says to Aurelio "the core should be lifted at least up to the level of the bench' ceiling". By the core is he referring to the base of the combustion chamber? Is this a general feature or specifically for that design? Does it help to lift it higher?

The word 'core' is referring to the entire combustion core, being the firebox and riser. For the right picture what was meant here, imagine the complete combustion core would be on top of the bench. The comment you are referring to is specifically meant for what Aurelio intents to build. Namely, a long bench at one side of the main bell and the exhaust at the other. In order to create enough space for the gasses to reach the exhaust opening, the space under the core should be mostly empty. This is an a-symmetric design, unlike yours.

In general, it helps to lift the core in such a way the space inside the bench is extended under the core as well. The Mallorca build was different in this respect being a 6" core only, so the main bell couldn't be too large. But behind the core of that specific heater there happened to be enough space to let the gasses stream freely so the core could be placed relatively low. The main bell could be built relatively low as well as a consequence so there was more of the ISA left for to implement the bench.

As a whole, it's a lost cause to try to incorporate all the features of several different designs into one heater. Concentrate on yours, you have been at my place for as much as 4 hours to ask all the questions you might have. I checked your drawing, maybe it would be a good idea to use bricks for the barrel support instead of using hardware cloth and lots of cob to close it?

Tuve Lundberg wrote:My main aim is to store heat. My current stove doesn't do that.
My (limited) understanding was that a heated seat gives so much more efficient heating than radiating the heat into the room. Will a single bell  keep the house warm 24 hours on only one firing?

That depends on the size of the system, the brick bell should be matching the size of the combustion core. Larger core, larger bell and therefor larger mass.

Peter van den Berg wrote:Please don't build a piped bench, if at all, coupled to a batchrocket system. This specific combustion system is very picky about friction in the smoke path...

Tuve Lundberg wrote:That's a disappointment...
No thermal mass, no heat storage? Or does it do that another way?

With a batchrocket, there's no need for a barrel at all. The mass of the thing could be in a single bell, double bell, bell and bench, whatever. For example, a 150 mm system could be housed in a double skinned brick bell, lots of mass. Let's see... which could weigh in at anything between 2000 and 3000 kg. In case you aim for a 24-hours heater, the mass in that bell would be best above 2500 kg, 100 kg for every hour of slow heat dissipation.

Of course you could choose to charge the heater with a single batch morning and evening in freezing weather. Or build a slightly larger one, say 180 mm, and charge that with one batch per 24 hours or two batches back to back when need be.

It might be a good idea to study the batchrocket website. Most information is there, including drawings and examples. The link is to the English version, the site is in nine languages although to date nothing in Swedish.
Lots of information to digest, also how bells work.

Tuve Lundberg wrote:How do I choose a suitable dimention for the needs of my house? It is only 44 m².

Hi Tuve,
This is greatly depending on your climate, the orientation and insulation of your house. A 150 mm batchrocket system is able to deliver about 20 kWh per batch of 6 kg of bone dry fuel. This 150 mm is the diameter of the chimney and riser at the same time.

Tuve Lundberg wrote:My house is small, and the space for the burner part is limited, how compact can they be, and how close to a plywood wall?

Since the house is small, a single bell might be better than a bell/bench combination. My heater is about 10 cm away from a wood stick/ plasterboard wall. On the wall behind the heater is a steel corrugated plate mounted on spacers. While the heater warms up the plate, an air current will start which in turn cools the plate. When my heater is too hot to touch this heat shield is still about hand warm. Works wonders!

Tuve Lundberg wrote:I was thinking the thermal mass could replace my current sofa, but due to the geometry of the room and placement of the current chimeny, maybe I should make a corner sofa out of the mass. But then the pipe length would be something like 11 metres. I have no idea if that is too long.

Please don't build a piped bench, if at all, coupled to a batchrocket system. This specific combustion system is very picky about friction in the smoke path.

Tuve Lundberg wrote:I live in a climate with wet, foggy and windy winters, temperatures most of the time slightly below or above freezing. I think I need some way to help the draught start in the right direction.

As long as you run the heater every day you'll find there won't be a problem. Lighting a warm heater is the easiest, by far. You might get problems while drying out the heater and further down the timeline, starting up a stone cold heater in autumn. A bypass would be a very handy in this regard.

Tuve Lundberg wrote:And how do I stop the draught pulling the warm air out of my house between the fires?

Close the heater's door and the air inlet. See that you'll get a tight closing door and there'll be no problem.

Tuve Lundberg wrote:I read about batch boxes today, and I can see how one anxious teenager in the house is really going to be relieved at having a closeable door. The open hole would freak them out.

Batchrockets are very reassuring in this regard, it can be loaded and top lit very safely. Basicly it's loading, lighting, closing the door, seeing and hearing that it comes up to a healthy burn and walking away. Easy peasy, sort of.

Tuve Lundberg wrote:Please, be my guides on these first steps of my journey! Assume that I don't know the american names of materials and components, as I'm Swedish. I may need just a bit more detailed explanations of special words. Please bear with my metric brain...

I am from the Netherlands, ISO system is what I grew up with.
Question from my side: what's the diameter and height of your existing chimney? Is it straight, cylindrical, smooth inside and higher than the top ridge of the roof? No other buildings or trees nearby?

The core is slightly scaled down to 5" as I understand it, which is very close to  the 125 mm dia of the chimney. It might be that the initial difficulties were just teething problems, such as a wet heater. Give it time, within 4 to 6 weeks of running on a daily basis the thing should be dried out completely.

Having two 45 degree bends in succession shouldn't make a huge difference, if at all.