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7 inch batch box rocket mass heater in the woodshop at wheaton labs

paul wheaton

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posted 2 years ago

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At first, we had the cottage rocket. It was okay, but it was struggling with the stratification chamber. It was an early version and needed some improvements - but even with the improvements, it would still take a long time to warm the space. It has been moved to the dog star where it is doing great.

Then we had the liberator. The liberator performed exactly as designed. The liberator is at its best with pellets, but can do a good job with sticks. In our shop, the space gets very cold when nobody is in there for a few days. And when we have work to do, we want to heat the space quickly. The liberator is designed to keep a house warm - to raise the temp in the house ten degrees in an hour. The wood shop needs to raise them temp about 40 degrees in half an hour.

Mud and I talked. A full 8 inch j-tube could raise the temp in the shop by 40 degrees in about 60 to 90 minutes. Further, there is currently no insulation between the wood shop and classroom, so whatever we do will take longer as the classroom ends up being heated a bit. And in the winter, when there is class, it would be convenient to hit both heaters in the morning to heat things up even faster.

To heat faster than an 8-inch j-tube we need a batch box rocket mass heater. Triple barrel. So one barrel over the riser, and two barrels as a stratification chamber.

The door is a "plunge door" - kinda like a casserole door that is more likely to last

(from grey's thread)

(from stephen's thread)

(from caleb's thread)

batch-box-fire-glass.jpg

batch-box-fire-glass-door.jpg

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paul wheaton

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posted 2 years ago

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Still some work to be done.

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paul wheaton

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posted 2 years ago

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One of the problems we have seen with batch box systems, is the untrained operator would accidentally plug the port in the back or the port in the front. This design seems to do a pretty good job of preventing either of those issues. There is metal tube at the back that prevents wood from getting loaded near the back port - and the slope of the door prevents wood from plugging the front port.

But ... I do have a cocern that could turn out to be fully mitigated. The metal tube is gonna get freaky hot. A stainless steel tube set in a steel holder. The temps will never get hot enough to melt stainless steel, but the temps will get hot enough to make stainless steel soft and slumpy. But this could be fully mitigated by cooler air moving through the pipe at that critical time - possibly cooling it enough to keep it from slumping.

The mild steel that holds the stainless steel could spall at 1600 - but there will be ash on top of it that will insulate it from the fire a bit - plus the cold air moving through it could help.

Mud mentioned that 8 inch batch box systems saw the pipe get soft and would need to be replaced. But 6 inch systems did not have that problem. This is a 7 inch system - so time will tell if we are okay.

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thomas rubino

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posted 2 years ago

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The steel secondary air tube is indeed kept cooler by the incoming air.
The layer of ash is an excellent insulator.
My 6" and my 7" batch secondary air tubes are still solid after two years of extreme high-use burning.
I expect them to last indefinitely.

I see you are using a stainless steel riser stub, this will definitely outlast a plain steel stub.
A carbon steel riser stub is expected to last one season or less.
They lasted apx. twelve weeks in my shop stove before badly spalling and needing to be replaced.
Using the D.T. quick-change secondary tube, changing stubs is quickly accomplished.
Your stainless steel stub will outperform the carbon steel by quite a bit.
A further upgrade from Stainless steel to an RA330 stub would be a lifetime improvement.

Excellent job by Mud, Issak, and the crew!

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paul wheaton

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posted 2 years ago

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Tom,

Howzabout a stainless liner for the inside of the door? So the fluffiness is not exposed to the fire as much?

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paul wheaton

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posted 2 years ago

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Peter van den Berg wrote: It seems to be unclear what size of system this is. Sometimes it's called a 7" system and sometimes a 6". The 3 barrels together is regarded as the top limit for a 6" system so maybe it's a 7 incher? I'll follow this one closely to see how it'll work out.

It is a 7 inch system.

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thomas rubino

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posted 2 years ago

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I think warping might be a problem with sheet steel on the inside of the door.
I experimented with using an insulated piece of 1/8" RA330 sheet as a roof covering, it was warping in no time.
Yes, the roof temps at the back are significantly higher than the door temps would be.
If you have SS sheet on hand, tacking a piece in place would be a good experiment.
If it warps cut it off.
If it works, I will say thank you and incorporate that improvement into my pop-in doors.
If the concern is the exposed Morgan, it could be replaced with CFboard.
Although I would think that door temps are low enough to not affect the Superwool and change its composition as it does inside the riser.

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thomas rubino

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posted 2 years ago

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I'm curious, what was used for the roof on this batch?

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paul wheaton

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posted 2 years ago

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thomas rubino wrote:I'm curious, what was used for the roof on this batch?

Lots of pics taken. Unfortunately, i can't seem to find any.

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paul wheaton

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posted 2 years ago

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fresh pics from caleb's thread

nothing but steam

still just steam

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paul wheaton

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posted 2 years ago

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I walked down to the wood shop and on the way i could see the exhaust for this. Zero coming out. So I was certain that nobody was in there - because it is a cold day and surely they would want some heat. Maybe the fire went out? I got inside and saw there was a fire burning. It was just burning THAT clean!

Here's a pic that Caleb took yesterday

I think it would be nice to add a handsome plaster layer and buff that first barrel a bit. But it's a shop ...

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david higos

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posted 2 years ago

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Hello,

I really like the front part of it not just because it helps with possible wood clogging but because it simplifies the door problem.

Is there anything like perlite in the cob mix surrounding the burning chamber/ any other alike insulants? Is it good enough to have a wide cob wall (guess cob mix rich in sand) surrounding it? Would it be a good idea to add expanded clay to cob to surround the burning chamber?

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posted 2 years ago

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hello,
...I would also love to know if you would recommend to make the burning chamber slightly larger at the bottom to accomodate the gradient of the door (keeping all other dimensions as the tables say) or to keep the volume of the burning chamber constant by reducing the depth of the ceiling by the same amount it is enlarged at the base.

paul wheaton

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posted 2 years ago

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I should mention that the plunge door came from here https://dragontechrmh.com/

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paul wheaton

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david higos wrote:Is there anything like perlite in the cob mix surrounding the burning chamber/ any other alike insulants? Is it good enough to have a wide cob wall (guess cob mix rich in sand) surrounding it? Would it be a good idea to add expanded clay to cob to surround the burning chamber?

No perlite.

Normally, I would say that it would be wise to add more insulation here. At the same time, it is burning very clean - so I guess I need to say that adding more insulation here would be optional. I think adding a bit more insulation might give you a few seconds of an even cleaner burn at the beginning and ending.

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Peter van den Berg

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david higos wrote:I would also love to know if you would recommend to make the burning chamber slightly larger at the bottom to accomodate the gradient of the door (keeping all other dimensions as the tables say) or to keep the volume of the burning chamber constant by reducing the depth of the ceiling by the same amount it is enlarged at the base.

What the tables don't say: the firebox depth could be enlarged by as much as 25% without compromising complete combustion, at all. In fact, the firebox is acting as a tunnel, volume isn't really the factor that drives it.
So I'd recommend to enlarge the firebox at the bottom until you've got the asked for 45 degree angle.

regards, Peter

Coydon Wallham

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Any measurements of the exhaust temperature going up the final pipe?

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Chris McClellan

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posted 1 year ago

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Coydon the surface of the final chimney is around 175 degrees F.

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Coydon Wallham

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posted 1 year ago

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So three 55 gallon drums is the magic number? Is the stratification chamber a version of something from the Cottage Rocket book?

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Chris McClellan

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posted 1 year ago

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Here's an update on this batchbox.

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posted 1 year ago

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Coydon,
Peter knows better than I do the limits of this design can handle being slowed down by stratification chamber. I took an educated guess and it worked. We do have the benefit here of a 25 foot chimney for lots of draft. The double barrel stratification chamber has been used by a lot of people but this is the design in my CottageRocket book.

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Peter van den Berg

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posted 1 year ago

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Hi Coydon, as Mud said, this is about the limit this system could handle. Which in this case is about 5.06 m² (54.5 sq ft) of Internal Surface Area (ISA) of all three barrels combined. In this heater, some of the heat is absorbed by the core and radiated into the room. The design scales up very fast, the maximum power and thereby the maximum heat extraction is dictated by the amount of fuel what the firebox can hold. In this case, with the firebox outside the stratification chamber(s), the ISA is not as large as it could be as compared to a brick bell that contains the entire core. In that last case, it would be 7.6 m² (81.8 sq ft), according to the table and Benen Huntley's rule of thumb at the foot of that page.

Also, see my own workshop heater design, the three barrel tower, which is driven by a mere 15 cm (6") core. It's fair to mention that the exhaust is placed about 20 cm (7.8") from the floor, so the gases are extracted somewhat higher up in the tower.

Regarding this woodshop heater: all boxes are ticked. The plunge door is a good idea to avoid work on a doorframe, hinges and fixings to the core. The floor channel is correctly implemented, during the burn the secondary air inlet will gobble up more air at the cost of primary air, exactly the right mechanism. What I probably would do differently is the placement of the exhaust pipe. A bit higher up in the barrel, so gases would be able to enter all around the circumference of the pipe.

Apart from that: a nice implementation, and it works! I would regard 75 ºF as a bit too warm for a workshop, though.

regards, Peter

paul wheaton

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posted 1 year ago

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more pics from dez

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posted 11 months ago

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Paul just published a video on Youtube about this Rocket Heater. Yay for spreading all the Rockety greatness all over the internet!

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posted 4 months ago

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The arch:

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paul wheaton

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posted 3 months ago

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A bit about the plunge door

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posted 3 months ago

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Cob for the triple barrel batch box rocket mass heater:

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L Cho

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posted 2 months ago

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I like the idea of the plunge door, but I have questions.

Is there a minimum angle, from perpendicular, that is required for reliable closure? How thick should the steel be? What method is used to attach the insulation?

thomas rubino

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There is no set minimum angle, just common sense allowing gravity to keep it in place.
I believe that door used 1/16 angle for the frame and 11 gauge 1/8" for the plate.
Heavy automotive cotter pins were welded to the door skin and poked through the superwool.
Each build is a bit different as I try new ideas.
For some builds I used 2 " straps diagonally welded to hold the insulation in place.

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Chris McClellan

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L Cho, Thomas is being too modest. I designed this heater around the fantastic door he built for us. He can build you a door or he wrote this handy book on how to build your own door. https://dragontechrmh.com/how-to-build-a-batchbox-door/

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The steel air intake:

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L Cho

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My village has an old factory converted to a performance space. The building is uninsulated concrete, and new for me, has concrete roof framing, that seemingly looks formed in place. I proposed to warm it with a rocket heater during performances, and the organizers have added it as a project in their plan for next year.

A massless design would be ideal, as it is a large space, used infrequently for short periods of time. Barrels can be a little hard to find here, so I was thinking about fuel oil tanks, which can be had for free. If the tank can be cleaned/purged enough to be considered safe, can I simply adjust the value of internal surface area, ISA, by raising or lowering the exhaust port?

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L Cho, another rocket builder here, Scott Weinberg, and I were discussing a month ago repurposing an old fuel oil tank turned on it's side rather than using barrels due to a height restriction that he had in the space that would prevent him from double stacking drums. As you point out, proper cleaning would be critical. Please keep the community informed of your progress as you continue your planning and consider starting your own planning/building thread so we can follow along.

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L Cho wrote:A massless design would be ideal, as it is a large space, used infrequently for short periods of time. Barrels can be a little hard to find here, so I was thinking about fuel oil tanks, which can be had for free. If the tank can be cleaned/purged enough to be considered safe, can I simply adjust the value of internal surface area, ISA, by raising or lowering the exhaust port?

That's what I did to find out the optimum ISA for my three barrel tower. At the back, out of sight, there are three holes, two of them blocked at the time the picture was taken. At the bottom was too much, about 60 cm (2 ft) higher turned out to be too little. So, definitely affirmative, the optimum ISA could be tuned by lowering or raising the exhaust port in the barrel or whatever tank you are using.

regards, Peter

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posted 2 months ago

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L Cho wrote: Barrels can be a little hard to find here, so I was thinking about fuel oil tanks, which can be had for free. If the tank can be cleaned/purged enough to be considered safe, can I simply adjust the value of internal surface area, ISA, by raising or lowering the exhaust port?

An old fuel oil tank is exactly what I used. A 300 gallon tank has just about the perfect ISA for a 7" core. DSR2 in my case, so it could slide in.
https://permies.com/t/151576/Sherman-Tank-DSR-Rocket-Mass

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Wow, this is some great documentation and great innovation.
I love the three barrel tower to maximize surface area and quick heat.
An interesting connection of a firebox configuration which is normally coupled with a mass heat exchanger but this time connected to a large "massless" surface area.
Keep up the good work!

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