Huge batch box rocket stove

Hello. I have built a huge batch box rmh.its a 12" system. I built it to heat an 30' ×96' gothic arch greenhouse. Living up here on the  Tug hill in  northern new York the winters can be harsh. It took almost a month to build and and is the second attempt. First one a failure. I finished this one and have been running it about two weeks now. Still made a few mistakes but minor. I'm going to fix them this summer. Three nights ago it was -15. I had to fill it three times. 3pm,9pm and 3am.about ten large pieces of wood each fill. It ran  HOT. Maintained 60° all  night. I'm impressed. It's the same size wood that I burn in my classic outdoor stoves which would have taken about 45 pieces of wood in three fills and probably would have kept greenhouse around 50°.We have 15,000 sq ft. of greenhouses and they will all have rmh in them as fast as I can build them. I'm not done with this one. I still want to make a heated  corner mass sitting bench. Sky's the limit with these rmh. Probably a bench to propagate in one of the houses. Thank you for all of the informative you tube videos.

Welcome to Permies, Eric! That's an impressive build. We would love to have more details, and dimensions for the record. Any mistakes and how you fixed them, and lessons learned, would be especially valuable.

Hello. First mistake is top load. It's to darn hot to open it once full of wood. Solution is go up two or three more courses and and put a door above ash door. Going to make an oven on top with fire brick. Summer project. To get me through the winter I'm going to put ceramic fiber board insulation on bottom of door. The lid is already crazy heavy so definitely not the best fix. Next a ceramic fiber board baffle directly above the riser. I  shut it down to cool yesterday and fixing them today. The lid and above the riser. Started out with  grates to high at 10" and lowered them 3". That fix was easy. The bell is 4'×4'×4'. The riser is 44" tall 12" inside. Three inches of ceramic fiber blanket parged with sakrete high heat mortar. The  batch box inside is 24" deep 32" across and roughly 32" deep. I will have more pics later today. Thanks

Assuming a couple of things: you built it with a grate and air provision under it? Better over the grate instead, nothing at all through the ash pan level.
The  batchrocket's proportions are quite strict, it would work much better when one is adhering to the recommended values. It amazes me it works like this anyway, it has something to do with wall area versus volume ratio which is getting more favourable in bigger versions. The port seems to be the right proportion to the riser, though. You found out yourself the top deck of the thing will get awfully hot in your construction. This design is real tight, build it as recommended and it will work as it says on the tin. In fact, it doesn't act much like a wood stove, more like a wood gasifier instead.
Good luck!

Thank you for the reply Peter. I mainly watch you and Paul and bro audio on you tube. I don't know why I never went to permies.com. no one in my area has built a rmh that I know of especially a big one. Is there a  size limit where it changes to something else. I don't get off this hill very often. Please explain build it as recommend and it will work as it says. I feel like this works. No  smoke only at first 15 minutes. Exhaust is consistantly around 169°f- 190°F. it rockets. And once it's warmed up I can burn any kind of wood I put in it.thanks again. Feel free to ask me questions.

Eric,

I think your build is amazingly successful. I've been watching builds like yours for at least 10 years and none have worked that well in my opinion. Yours however seems to do exactly what you want it to, heat a large space efficiently.

I'm of the opinion that there are way more options on building a successful rocket stove heater than have been discovered so far. I believe we are just in the infancy of this wonderful technology. You've shown that there is a least one way that had not been built before and it works.

I like the idea of your insulation over the riser so that the roof of the bell doesn't get the direct blast of hot combustion.

Please continue to update us on what you are working on. I for one am fascinated with your work.

I have a couple of questions Eric,

It looks like your bell is just a steel box, and then there is another galvanized box over the top that you use to extract the heat with the squirrel cage fan to push the heat into the green house.

Is that correct?

How do you lift the galvanized box to access the steel bell that we are looking at in your pictures of the riser?

Correct. Me and a friend just lift up and slide it over. It's called a plenum and it's more bulky than heavy. I've decided this is a rocket mass furnace. Rmf. I  seen an oil furnace with a plenum and duct going of every direction through out the house. That is where I got the idea to put on it on the  bell with a  blower.

Thanks for clarifying. That is truly awesome. Without that new picture of the firebox with the slabs in it I was having a hard time getting a feel for the scale. It really is HUGE. Great application and extrapolation of the rocket design.

One more question: What is the device sticking out of the front of the steel door at the bottom of the firebox? I'm guessing it is some sort of air inlet but it appears to be cast.

And I wish you were closer. I'd love to see that beast running. I looked up the Tug Hill. Quite remote. Not what most folks think of when you say New York.

Thanks again Duane.it is the air inlet with a electric selinoid hooked to a thermostat to open and shut as needed. And yes we're out in the country and love it.

Duane, here's a couple more pics.

Duane, here's a couple more pics.

Just wanted to let everyone know I put out a video on YouTube it might help to see how big it really is.

Found the video!

Thank you.

I'd love to see a video of lighting it and then dumping wood in.  

Also, seeing it with the plenum removed might be nice.  

So how long does the fire burn and then how long after that does the "mass" keep giving off useful heat?

I'm assuming that's a double poly inflated house?

The  concrete part with just coals remaining from previous fill a good 12-16 hours depending on outside temperature. The bell with no blower will just keep going up until coals are almost gone. And that is with air shut during the day when greenhouse is warm. Fill times depend on outside temperature. Two nights ago it was 35°f I  put ten pieces of wood at 4pm and never put wood in until 5am only four pieces. I'm still learning burn times. It's probably going to take this year to learn about this thing. And yes its double poly 6 mill sun master. Thermax inside layer. Here's a pic of first stove I reused the bell.thanks again.

Eric, that is a beast of a batch-box:o)  I've burned yellow pine in my 6" batch-box, and it burns crazy hot compared to hardwood. Pine just doesn't last as long, but it generates a whole lot of heat very quickly, tending for the whole load to be catching fire all at once when the stove is already warmed up to operating temperature. Might try a third to a half load of pine to see how it does first, while keeping a close eye on just how hot the steel top loading lid gets.

About the front loading door, mine is cast iron and gets uncomfortable to sit within 4 feet of whilst the batch-box is running full tilt. I noticed how Matt Walker constructs his front loading doors with CFB for insulation. I'm thinking of making something similar for my batch-box.

Anyway, looking good!

Definitely going to insulate the  next door with ceramic fiber board. This door is to warped to fix it. Just going to ride it out the rest of this winter. Starting to get really busy in the future weeks.

Eric, That video is great at showing the size and scope of your ROCKET stove heater. That's like the Saturn V compared to the Atlas II that the rest of us work with. The thermometer pics I assume are the sides of the bell, but the small window could use some explanation. It looks really hot wherever it is.

You certainly have your work cut out to run a producing farm and build several more HUGE rocket stove heaters. I hope you have plenty of help. I'd be there but I'm allergic to NY, old, and fairly busy myself. But I'll be cheering you on from Northern AL.

I would think that a side door may work better than a front door because it would be easier to toss the wood in inline with the long direction of both the fire box and the logs/slabs rather than the short one. The door could be smaller and you might even find a wood stove door or fireplace insert door that would work saving a lot of effort to build one.

I'd also look into putting the primary air inlet above the normal fire height like Peter recommended just so ash doesn't get in the way if you are going to run it for a couple of days at a time if you get the feed design worked out.

A full width ash pan might be in order as well so cleanout can be trivial. I made mine out of 1/16 galvanized and Kast-O-lite 30 LI Insulating Castable Refractory: with a 2"  lip and then just built up the edges leaving the center 1" thick to form like a burmed pond to hold the ash. Just make it so the sides of the pan extend to the exterior walls and are under the insulated portion of the walls so the metal is not exposed to the fire itself. Yours would need to be scaled up to be deep enough to hold enough ash of course. I've been running my stove hard for two winters and the ash pan looks like new even being the floor of the 1700*F  firebox/burn tunnel for up to 5 hours at a time. A couple of handles welded to the front and you'd be able to clean the ash in less than 5 minutes.

You might look at the way they light TLUDs to make start up a little easier. Top lighting of fires is done extensively in places like India and can be quite efficient. Just requires a slightly different technique. As for me, I'm a big fan of charcoal briquets saturated with Kingston lighter fluid; easy and fool proof.

Please keep us up to date on your progress. And thank your wife for the taping of the video.

Good morning Duane. Thanks for the input. Still thinking a door on the front. With the arch I'm putting on top  I feel I can put a taller door. I would like to continue burning the bigger wood. I feel it lasts longer and less time cutting and splitting. As of this year I'm burning around 100 face cords of wood. A few years ago we were up to  150 face cords. 20-24"long we've made some adjustments to get to this point. Now hoping rmh will get me down to 75 face cords. Sending a pic of roughly where the arch will be. Thanks again and enjoy everyone's thoughts.

But if put the door on the side it still could be big enough door for big wood I think. And put a bigger oven with that door in the front

That would make one awesome pizza oven, perfect arch style. I haven't looked but a furnace door from one of those outdoor hydronic furnaces might fit the bill as they are made to take quite large logs. And if the air intake is relocated higher you won't need the grate in the bottom either. Simple is better, especially if you have so many to make and feed. Your summer is going to be busy, but fun.

Your the second person who  suggested to find an old door to use from an outside boiler for this project. Thanks

I do see a potential problem with making an arch over the firebox. In thinking about the super clean burning high performance design of Peter van den Berg's batch-box, and that it depends upon straight-line primary airflow through the fuel wood pile to the port. Ideally, and as recommended, the fire is lit near the port and burns from the port end of the wood pile back towards the primary air intake. Incoming primary air flows through the wood pile (firewood loaded lengthwise having one end near the primary air intake and the other end facing the port, which is why the fireboxes are naturally constructed long and skinny).  Combustible gasses don't linger inside the firebox, but are essentially "piped" directly to the port for secondary combustion inside the riser.

Adding the arch, increasing the ISA of the firebox, introduces extra area for the unwanted buildup of combustible gasses. The danger is when those gasses flash off inside the firebox, pressure instantly builds, to much for the port to handle, thus the stove belches smoke and fire out of the primary air intake. In the worse case, the processes repeats itself in a cyclic manner.  

Better to stay with the intended batch-box design, go for a hotter faster fire, and store the excess heat in masonry mass. That's really to best way to conserve on fuel-wood.

Duane, are you allergic to the cold or our goveneur. Lol.😎

I think your firebox is already bigger in proportion to the system size than the standard, and increasing the volume as much as that arch indicates may give problems as mentioned.
"The batch box inside is 24" deep 32" across and roughly 32" deep."
Extrapolating from the chart, a 12" batch firebox should be about 18" wide x 26" high x 36" long.

Given the long pieces of wood you show filling the current box, I think a door on the end would work better as you could put long pieces in without a huge door. I realize cutting out the reinforced block wall would be a job, but I think the results would be worth it.

One thing that puzzles me is the port in the middle of the long side - how does the wood stay clear enough of that for proper airflow and the venturi effect? Or does it?

As you are planning to build more of these, I think it would be a really good idea to make the next one with standard proportions and the port on the end, so that you can test the operation of the stock model. I would also make the bell with some masonry, like for the walls, with a steel plate top for ease of roofing. The bell does not benefit from maximum volume but maximum surface area, so if you made it long and narrow, say 2' x 4' x 7' high, you would get the same heat transfer with less space taken up on the floor.

So glad I started this thread here at permies.com. thanks again for all of your suggestions and input. I can see I still have a lot to learn about rmh.

Question for you Eric, it looks like you have a short but significant burn tunnel between the firebox port and the riser. What are the dimensions of the tunnel and why did you build it this way? Ok, so that is two questions.

Tunnel is 9" long and 4" wide 22" tall. The riser is 12". I figured it would be narrow enough to create the draw I needed for the size of the batch box. I didn't have anything to go by except what pics I've seen. And how in one of the videos think of it as a creek that narrows then opens up when the creek is narrow  the water is faster. Also the chimney is 8". I tried to match the cubic inches of chimney with  ash door  draft and figured the closer I got the fire to the riser the better.the first stove was a 6" system and was a 30" tunnel to the riser. That's why I did it this way hoping it would work. Thanks again. Another-15 last night. 50 by Wednesday. Anyone ready for summer yet. Another problem with this. The wood constantly hung up and fire would burn out if I didn't catch it in time.

Hi Eric, thanks for sharing your design, you have done a great job and the fact you are happy with its performance is the most important  thing.
So in fact your chimney is 8’’ ?
I love the fact you want to build more of the same but, my suggestion would be to build one of Peters designs as it would be very interesting to see how the units compared with each other.

Another question, (I know I'm a pest), if you've had the bell open since you started using this stove in a big way, did you find much ash on the floor of the bell?

I'm totally fascinated by your stove because it is the first one I've seen that can heat almost 3000 sq ft and with marginal insulation by typical home building standards. I wish some engineer out there would calculate the energy required for that many cubic feet. Also, yours isn't really a Rocket Mass Heater but just a Rocket Furnace because you don't really attempt to store any of the heat in a mass but rather are heating the entire envelope. But still you don't waste much because the stack temps on the chimney are very reasonable, not much escaping to the outside.

I am going to add mass. Just need time. Summer project. Hoping I can make a mass bench the whole length of the greenhouse. Could use the bench for propagation. Now I am using ken bar electric strips. They work great but electric bill goes up 500.00 for a couple months. Plus if power goes out you need a big generator to power everything unless you shut power off to the benches. Yes I have opened the bell to put ceramic fiber board above the riser. Very little ash. The first stove when I took side off of bell to put new riser in. I filled a 30 gallon trash can with creosote and ash.

I do have to say I did have help from a local welder and a fabricator on the first stove. All by my bad  design though .new idea. Put a door in the side. Fasten lid down better and put another plenum with another small blower on  top of it.harness even more heat. Then build a small one at other end of greenhouse for warming up left overs for lunch and back up for these super cold nights.

Hi Eric,
I now understand YouTube videos were your main source of information about batch box rocket heaters.
Maybe you didn't know before but there's a website about this type of heaters for almost 6 years now. It's translated in a multitude of languages, English being one of those. Please see https://batchrocket.eu/en

Eric, those photos of the smaller batch-box, the combustion unit (firebox) is way to narrow, and the port is no quit right either. From Peter van den Burg's site

https://batchrocket.eu/en/building#dimension

the batch-box can be sized by following the rule set just below the Peterberg Rocket Stove Calculations common sizes table, for greater than 10" system size batch-boxes.

Once you build one of these "heat machines" to spec., you'll be amazed at the performance:o)

Can I mention permies.com in my you tube videos. I have been wondering. Thanks. And I am going to take your advice and build a smaller one.

Yes, by all means!  The more links and mentions, the better to help spread the word.

I can definitely see I have more to learn. Especially if I start building more rmh. Maybe I got a little lucky on this build for it to work. Maybe it doesn't work 100% and I think it does only cause I've never been able to see one in real life and how it truly burns except for what I have constructed. Thanks for your advice again. And yes another video is going to be put out very soon. This time loading it and talking about how it runs.

Thank you Peter and Bryan for the links. Duane  you were wondering about the size unit recommended to heat a greenhouse this big. I asked an engineer. He says where we live 100,000 BTU's per 1000sq feet.so for a  30'×96' greenhouse with double poly 300,000 btu furnace is recommended usually talking about oil, gas,or propane .