EZ No Tools Brick Micro Batch Box Core (The Match Box) Plus Variations

I was messin around, playing LEGO and I tried the center Venturi into my original configuration.  My new firebricks are supposed to come in today, and I need them to complete any of these configurations.   I will try this for fun, and I will try the tiny 4" square riser also, when I get the new bricks.  

I'm not trying to copy or duplicate anyone's work.   I just enjoy these experiments I do on my YouTube channel and I enjoy sharing my experiences and projects here for you guys.   I also often seek advice here, but I enjoy and take pride in my own projects.  Like show and tell lol

I finally got my new chainsaw today for my belated birthday gift.   It's a monster, I thought I was getting a 46cc poulan pro, 20" bar, but I ended up getting a 50cc pro, 20" bar.   I just finished assembling it.   I'm not going to use it to kill living trees, I wanted one for my rocket mass stove projects and there are at least 10 dead elms dying or dead on the property, and one is hanging over my chicken coop.

50 cc is kinda heavy for a small 5'9 guy like myself, but it's gonna be a good workout also lol.  Maybe it's a little too big for rocket stoves and dead elms, but I could use it to make a badass Alaskan mill also.

My new firebricks are in, and I'm excited to go pick them up this afternoon!  Then I will be able to construct a full more proper riser and full core, for one proper full sized long burn test before I mortar it together.  

Well after I picked up the 25 kilo bundle of bricks in my PT Cruiser, I was feeling a bit like Pablo Escobar lol
It's funny the way they are wrapped up, these bricks

There seems to be a brand name on these ones...  Pacific Energy.  I got the bundle of 25 for 50$ and that's the best price I've found around here thus far.   Hardware stores sell individual bricks locally, but they are over 5$ each!   Anyway I'm glad to have these bricks and perhaps tomorrow I can do my full brick riser, full test.  If not tomorrow I will get something accomplished this weekend for sure.  

I've attached a photo which is kind of vague

we got snow today here in Ontario!   its not pretty

here are some final variation/final test videos from the other day using the stronger dense bricks for a sturdy firebox, and the lighter more insulative ones in the riser and venturi areas...  i also took peter's advice and made a center venturi port, resulting in the desirable ram's horn vortex

episode 49


EP#50!  my 50th rocket stove video, and my 199th youtube video!

John, this is quite the same track I was following in 2012. Two remarks though: the venturi port could be narrowed down more and in my experience the grid isn't doing anything to improve combustion when using a centered venturi.

And you are right about all the leaks, it will result in sub-optimal behaviour.

The venturi will always work as long as the cross section area is quite a bit smaller than the cross section area of the riser. In my designs I used 70%, but at some point I tried smaller ones, even down to 50% and the thing kept working nevertheless. Reliability is becoming an issue in that situation, though.

thanks again for the help and input peter.
i agree,
i was aiming for a 2" venturi (2x9) but i did not measure it for the test fire.  i did shift them tighter during the final test fire but i could not make much difference as you said, the air gaps and leaks everywhere were not optimal.   the only thing i have left to do now is actually install it.  i had planned on installing this Batch box, or the cast-core model, into my earth-berm concrete 20x20 tiny home.

By the way, I think the term Match Box Rocket Heater is a fitting (and funny) description for a 4" or smaller appliance.

Agreed, it's an appropriate, relevant, and comical title.  

Plus there are other considerations to give it a slightly different name, at first I was told that what I was building was not a batch box, so I had to call it something hahah.  Micro + batch = Match box.  

We ended up getting even more snow overnight last night, but temps are supposed to go above freezing this weekend thankfully, because I'm not yet prepared for snow!  
:p  

I'm planning on using this for a base, they are 4" blocks and they have "air gaps" that I'm told I should have underneath.   Should I mortar them to the floor?   Should I butt them up against the concrete wall?  Theses are not exterior walls.   I think it seems best level with a slight gap around the walls.   I was going to make a 4ft long base, but my small space restricts me so I'm going to make it only 32" long.   It's going to be tight but if I use the 30 gallon barrel as I wanted, it should fit fine with 5" or more all around the barrel, and perhaps heat up my wall a bit like a mass.   Input?

John and Peter -
Your conversations, photos and videos have been so very helpful to me!  Earlier today, I posted a request for information about a PORTABLE rocket WATER mass heater.  Glenn answered with some helpful suggestions, but I was wondering if this Match Box Batch Box would work with what I'm considering.  Also - is it possible to use a VERTICAL feed on a batch box?  We're in our 70's, and since we'd be installing this in some form of box (like the boxed gravel/rock fill), a horizontal feed would be difficult.  Any other suggestions you might make to help?
Thanks for all the time you nice people take to help others!   I'm hopeful that I can cut our $400/mon electric heating bill down a lot!  We're surrounding by woods - so it makes sense to use 'dead fall' for heat!  Once again, thanks!

Linda Questor wrote:John and Peter -
Your conversations, photos and videos have been so very helpful to me!  Earlier today, I posted a request for information about a PORTABLE rocket WATER mass heater.  Glenn answered with some helpful suggestions, but I was wondering if this Match Box Batch Box would work with what I'm considering.  Also - is it possible to use a VERTICAL feed on a batch box?  We're in our 70's, and since we'd be installing this in some form of box (like the boxed gravel/rock fill), a horizontal feed would be difficult.  Any other suggestions you might make to help?
Thanks for all the time you nice people take to help others!   I'm hopeful that I can cut our $400/mon electric heating bill down a lot!  We're surrounding by woods - so it makes sense to use 'dead fall' for heat!  Once again, thanks!

Thanks glad to help I suppose
I do t know much about water but Glenn is a knowledgeable guy.   The closest thing I've ever seen to a vertical batch box is a stove built by FStyles, a fellow forum member here.   He calls it a rocket mag, because it has a large magazine, like a machine gun lol.    But check out FStyles comment above and click on his signature link to his rocket mag, if you are interested in vertical large load/batch load ideas.

Thanks, John.  I'll check him out!   ;D

John McDoodle wrote:I'm planning on using this for a base, they are 4" blocks and they have "air gaps" that I'm told I should have underneath.   Should I mortar them to the floor?   Should I butt them up against the concrete wall?  Theses are not exterior walls.   I think it seems best level with a slight gap around the walls.   I was going to make a 4ft long base, but my small space restricts me so I'm going to make it only 32" long.   It's going to be tight but if I use the 30 gallon barrel as I wanted, it should fit fine with 5" or more all around the barrel, and perhaps heat up my wall a bit like a mass.   Input?

Okay I talked to a guy who has been running cement bricks under his firebox for 2 years so I guess that part will suffice.  
Now I've been seeing these concrete block mass furniture ideas and I like them so much that I went ahead and purchased some extra 8" blocks, which I'm hoping to run a vent pipe through, and make a mass bench.   I'm planning on a 5.5 ft long simple straight bench, 16" tall, 16" deep, 5.5 ft long.   Is it okay to run a 4" duct/vent pipe through the bricks for 6 ft before exiting an exterior wall, and finally a vertical exterior exit.  This would be most simple and beneficial for me.   I've tested the core, and I've tested the core flowing through a 4" pipe, but I've never made a mass bench before.  I want to have a slight/smooth 6" funnel or transition between the barrel bell and the mass, which will be short.  I am lucky enough to have nice concrete floor and 8" block interior walls to work with.  The bench will be along-side a block interior wall, not an exterior wall.  

Does this sound okay?  I figured a simple one-way through the block-bench will eliminate any restrictive 180 degree bends, and should be a simple straight one-way pass-thru.

Here are some examples of simple 16"x16" concrete block benches.  I could build a whole bench like this and run my exhaust through it, or I could just build a hollow crib 16" high and fill it with gravel, but that seems like more work and i would have to find gravel.  

It might work to transition the outlet duct to feed both cores of the row of blocks, and recombine at the end to go to the chimney. This would have very little friction because of the larger total cross section. It is possible that it would extract too much heat from the exhaust gases, but may work well. I would feed the top row of blocks, as the heat would never make it up from the bottom row. Extrapolating from published bell internal area recommendations, a 4" batch box would probably support 25-30 square feet of bell surface. The cores shown would have about (4 x 4.5") 1 1/2 square feet per foot (x 2 cores), so 3 x 5 1/2' long gives about 17 square feet, leaving 8-10 square feet for the internal surface of the bell around the riser. That would probably not be enough internal size to fit the riser, though. Minimizing the height of the first bell would be key, putting the firebox low and the outlet at ~12" above the floor to feed the bench blocks. You might want to lay out the setup outside and see if it draws. If it does okay in a temporary setup, it will probably work better sealed up permanently.

My bell should be about 15" diameter and 27" tall max, but since my riser is 18" tall, my bell will likely be 20 or 21" to fit the riser.  Ultimately I could make a 27" tall riser with one more row, but I think the 18" from the firebox lid is fine?   The entire riser is already 27"-28" If you measure from the floor.  But my bell likely won't go down to the burn box floor, but rather likely sit on top of the burn box.  

I've tested the core, I've tested the core with a 14" bell and 18" riser, I've tested the 4" exhaust flow, I had about 200f-300F at the bell exhaust exit.  My main question/concern is about my mass bench idea.   If I stand up the bricks and leave the voids hollow, it won't make full surface contact between the duct pipe and the cement blocks, and there will be some air gaps between the duct and blocks.   I figure this might not draw enough heat from the exhaust, rather than too much.  A short simple straight hollow block mass bench shouldn't suck too much heat out I'm guessing.  If I filled a shell with gravel that might be the opposite, more contact with the duct and more heat loss into the mass.  But with the block bench, it's pretty much hollow with very little surface contact between the duct and the blocks...?

Don't use stove pipe in the blocks, because you need contact area to transfer heat to the bocks. Gravel has only small contact areas between itself and the duct so you need an awful lot of length to extract enough. Use the holes in the blocks as the heat transfer duct instead, I would say. You need to tie the blocks together firmly to provide a gas tight seal, other wise the CO will sniff you out.

On another note, the top gap between the riser end and the top of the bell should be quite a bit larger than the recommended minimum for a J-tube in order to function properly. The batch box design is vulnerable to resistence in the smoke path which lowers the gas velocity in the port which in turn will kill the complete combustion. That's why I am a firm advocate of the batch rocket / bell heat extractor combination. A bell system is sporting the lowest friction of all the extraction systems available at the moment, simply because it is driven by gravity instead of the gases rubbing the walls of a channel.

Peter van den Berg wrote:Don't use stove pipe in the blocks, because you need contact area to transfer heat to the bocks. Gravel has only small contact areas between itself and the duct so you need an awful lot of length to extract enough. Use the holes in the blocks as the heat transfer duct instead, I would say. You need to tie the blocks together firmly to provide a gas tight seal, other wise the CO will sniff you out.

On another note, the top gap between the riser end and the top of the bell should be quite a bit larger than the recommended minimum for a J-tube in order to function properly. The batch box design is vulnerable to resistence in the smoke path which lowers the gas velocity in the port which in turn will kill the complete combustion. That's why I am a firm advocate of the batch rocket / bell heat extractor combination. A bell system is sporting the lowest friction of all the extraction systems available at the moment, simply because it is driven by gravity instead of the gases rubbing the walls of a channel.

That's the thing, I don't want to extract TOO much from such a small system, or I won't have any convection at my final exterior stack.   Right?
I had considered just running the gasses through the blocks, but I wasn't sure if the mortar would cause excess restrictions, because I'm no pro block layer lol.  

So it would be okay to have a large gap between the riser and bell, and also be able to cook on top?   What is the minimum gap reccommendation for my 4.5" (x6.5") riser and 4" exhaust?  Perhaps a 5" gap?  I do not want many restrictions, that's why I was considering running the duct through the blocks, to hopefully avoid the need for air-tight and smooth block mortar joints, and for a smooth run with less restrictions.   But I can do it either way as long as the concrete and mortar do not eliminate my rocket draft.   I will see what I can do.  I have not yet done any mortar or permenant placement but I'm going to get some free lube drums this afternoon locally from a wanted ad I had posted.   They are supposed to have removable lids at around 25 gallons.  

Right, you need at least 60º C (140º F) at the end of the stack when the thing is running flat out. Any significant number less than that and you can foresee problems sooner or later. Whether you can cook on top is depending on how hard you push the thing AND the size of the top gap. In my opinion, the top gap in your case shouldn't be smaller than 2", provided there's space all around the riser end.

Personally, I would keep the gap on 2.5" in order to avoid the chance of restriction and still be able to cook on top. Keep in mind that the top of the barrel is able to dimple in due to the repeated heat cycle, so it would be best to choose the top gap even larger, 3" to be sure. When cooking isn't required I would keep that gap at a safe 5" or more.

If you keep the 4 1/2" x 6 1/2" rectangular riser, you will have almost twice the cross section of the 4" chimney, and the flow in the riser will be somewhat lazy, i.e. likely not very turbulent. This may reduce the combustion efficiency. (Similarly with the port - the full-height slot you tried will need to be much narrower to give a good vortex in the completed system.) Peter would be the one to advise on the minimum riser top gap for a 4" system. (Okay, he did that while I was writing )

I think the best bet for your block bench is to lay them tight together dry, and surface bond the exposed outer faces. The fiber reinforcing in the surface bond cement should keep cracks from forming or growing. Then you can plaster over the surface bond for a nice finished surface.

John its good to see you coming around to firebricks. There are two types of people that attempt to build rocket stoves... those that use fire brick and those that dont build rocket stoves. you know i gotta poke buddy. You and i know there are other ways, but fire bricks seem to work so well right?

I built my benches close to what you seem to desire. i basically built a cinder block outer edge of one block width and two blocks high and filled it in with cob and cemented the top on with portland cement. that allowed me to run the exhaust through the holes on the ends and fill in the center with cob with a cement top.

John you have seen how i built my system and you can see how close i used portland cement/perlite to my core and i have zero problems with this being my 2nd season with my system. i would entertain the idea of mixing perlite in with high heat mortar and use that between them to mortar the pavers to the firebrick and i wouldnt seen anything worse than what i have.

Thanks for the help guys.  

Glenn, I know my riser is slightly oversized but it is by design.   I've done a video of the core burning with the brick riser, and then I ran it through a 4" tube to test the core and 4" flow and burn efficiency.   If you watch the video it seems to burn good and clean even when flowing through an oversized riser and then a 4" pipe.   I was told to slightly oversize the riser because of the shape, also that's where the primary expansion happens.  Oversized compensates for shape, flow, and expansion, which I figured out in two of my rocket builds.  Also later on near the mass area the exhaust cools a lot and contracts, that's why it can flow through a 4" pipe.  My intake port will be no bigger than 4 square inches, so once the air cools near the mass, that's my max cold flow rate, whatever flows through 4 square inches.   It's impossible for more flow to come out than what goes in, after the contraction occurs.  

My only concern, and the only thing I haven't tested is a separate mass, and the convection loss involved there.  

I know I will have about 200-300F coming out of the bell exit, SO... can I go through a 5.5 ft mass after the bell and still keep convection?   How much heat will I lose through 5.5ft?   That's why I planned to use the duct through the mass, to keep the gasses flowing smooth and hot.   But this is my unknown zone, the external mass.  I have no clue how much heat I will lose there but with a one-way through, but the blocks are only 1-2" thick and hollow, so it should not take too much to warm them hopefully...    

I was thinking I could mortar the mass and blocks together, but not mortared to the floor, that way I can easily de-construct if something doesn't work...?   Unless anyone knows how much heat will be lost through a simple 5ft straight pipe, (4" diameter).  Although if I do not use a duct in the mass, it would be closer to 5" diameter because of the large voids in the blocks, which seems fine to help funnel down to 4", depending on the 5ft run heat-loss.

I can't tell you how much heat will be transferred to the block cores if you go without the duct inside; all I can do is extrapolate from the charts for bell sizes compared to batch box sizes which I did above. I do think that 5' of 4" duct (not built solidly into the blocks) is not going to transfer much heat to the blocks, maybe not enough to make them more than lukewarm.

John McDoodle wrote:I was told to slightly oversize the riser because of the shape, also that's where the primary expansion happens.  Oversized compensates for shape, flow, and expansion, which I figured out in two of my rocket builds.  Also later on near the mass area the exhaust cools a lot and contracts, that's why it can flow through a 4" pipe.  My intake port will be no bigger than 4 square inches, so once the air cools near the mass, that's my max cold flow rate, whatever flows through 4 square inches.   It's impossible for more flow to come out than what goes in, after the contraction occurs.

Yes, a square riser should be wider as compared to a round one. When the system is a 4" item and the riser round this should be a 4" size too. A square riser in the same situation should have a larger cross section area to compensate for the extra drag in the corners. Aerodynamically speaking, a square duct of 4" by 4" is as good as a round one of 4" diameter. But yours is quite a bit larger which could be alleviated by shoving the bricks left and right of the riser inwards in such a way that a square shape is achieved, by the look of the picture of your setup.

Just a suggestion, you are fully entitled to do it your own way of course.

John, the only thing i had wished i had done after i built my bench was to install vent pipes between the floor and the bench. i wish i would have laid down vent pipes and then built the bench on top of them so that air could flow under the bench and release some of the bench heat into the room. since my system is 6" i would have more vent pipes going from one side to the other than your 4" system.

F Styles wrote:John, the only thing i had wished i had done after i built my bench was to install vent pipes between the floor and the bench. i wish i would have laid down vent pipes and then built the bench on top of them so that air could flow under the bench and release some of the bench heat into the room. since my system is 6" i would have more vent pipes going from one side to the other than your 4" system.

F Styles wrote:John, the only thing i had wished i had done after i built my bench was to install vent pipes between the floor and the bench. i wish i would have laid down vent pipes and then built the bench on top of them so that air could flow under the bench and release some of the bench heat into the room. since my system is 6" i would have more vent pipes going from one side to the other than your 4" system.

I've heard about having air gaps and such below these cores and mass benches, and that's why I chose concrete blocks.   I can stack the 4" blocks two-high under the core, and I can use the 8" blocks on the mass, and flow through the top half of the blocks.   That way I get "air gaps" or passages below my core, in the base, and below my hot mass both.   I should really get sketch-up but my laptop keyboard is messed up since I've got it wet so I'm only using my iPhone right now.   I could show my ideas better than I can explain them.   But basically the blocks will be sideways and aligned so it creates passages in the mass and the core base both.

I was going to mortar the cement base blocks together for the core base tonight but I believe this regular mortar I have for the base may require sand to mix, so since I do not have sand here and it's late I will have to wait another day until tomorrow to mortar these together with the regular mortar.   I have lots of fancy high temp dry mortar mix and the high temp caulk type also, but I'm saving the good stuff for the core and the fire-brick areas.   Anyway here's some slightly better photos of the proposed core base with 12 four-inch blocks, 6 per row, two rows tall, and the air gap columns within

Okay it's the next day and I got the sand and made regular mason mortar.   2 parts mason mortar mix and 4 parts sand.   I also wet the mating surfaces and brushed on a watered down bit for better surface adhesion, then I layed an 8mm thick layer on the bottom row and levelled the top row as I set the top blocks on for the base.   Only one single block area had to be better mortar leveled after laying the mortar by eye.   So the top layer went on pretty level and then I parged the top again with a thinner wetter layer of mason mortar and gave it the broom finish.   Once it's dry I will likely adhere the next level with the high-temp mortar, thus the rough broom finish

Great block work so far buddy!

wheeew... its a good thing you pulled out your safety glasses to wear, i was worried.
I believe in building rocket stoves in flip flops and cutting wood dangerously. no safety gear required.

Progress?
It's going to be a tight fit but none of it is attached to the floor.   So it could be moved or adjusted if I need to.   I will be putting anothe 2-4" of pavers around the base also.  However, the entire base is all mortared together now into one piece, so-to-speak.  

Here's a few more photos.  

F Styles wrote:Great block work so far buddy!

wheeew... its a good thing you pulled out your safety glasses to wear, i was worried.
I believe in building rocket stoves in flip flops and cutting wood dangerously. no safety gear required.

Lmao that's hilarious.   I'm mostly concerned about the dust (mask) but I'm past that part now.  I'm not experienced at laying blocks but thanks.   Lego taught me lol.

Here's more photos of the core building progress.  My back stiffened up from bending over doing mortar joints so I took a break here.

Also notice in the pic, I dont need to split wood.

F Styles wrote:Also notice in the pic, I dont need to split wood.

Lol!
I didn't think that was actually you.   Is that actually you?  

John McDoodle wrote:

F Styles wrote:Also notice in the pic, I dont need to split wood.

Lol!
I didn't think that was actually you.   Is that actually you?  

No, its some random pic off the internet, but it was funny.

I still dont need to split wood.

That's awesome brother.   I cut up some dead elm round stuff the other day and it's small enough it won't need to be split.  Most of it.

Anyway here's photos of my progress from last night.   I really like this hi-temp mortar, it sets up nice and hard overnight.  

This is my smallest - tightest Venturi I've ever made.   It's 1.75" wide.

Do you have any more fire bricks? I am strongly suggesting making your batch box larger and deeper/taller. You will only thank your self for making it large enough to put in larger logs if you do. Also think about making it accessible with an air tight door on the top or the batch for a top down feeding and and air flow access in the front. Just imagine it before you finish it off.

For a 4" system (since that is the size of your chimney and will control the ultimate airflow rate), a 1 3/4" wide venturi is far bigger than likely optimum. Mine in my test was about 1 3/4" wide and half as tall as yours, and worked excellently with a strong vortex.

I'm sure it's tempting to increase the size of your firebox to go with the extra-wide riser and hold more wood, but there was a reason that Peter in his research settled on a certain ratio of firebox capacity to system size. If you have more wood in the firebox, there will be more burning at one time, and it may not all be able to reach full combustion. Also, the flames will not be able to move as fast as in a core sized to the chimney, and the lazy flow will create less turbulence for mixing. I don't have my own experiments to prove this, aside from knowing that overfeeding my woodfired kiln results in unburned smoke billowing from the top.

FStyles;
A removable brick at the top near the front would have been a good idea, but I finished the firebox roof before I read this message.  I have more photos.

I agree with Glenn, I better not do anything bigger than I have already tested.   Since my final exhaust will be only 4" (after my mass).  

So here's what I have done this far, and im sticking with the variations I have already tested and verified.

So far what I have done is very strong and rigid.   I really like this refractory brick mortar stuff, it's also premixed wet.  Once I mortar some pavers around the base and core it will look slightly better, and rigidize everything even further, but I'm not aiming for a beauty pageant win.  

More photos,

I still have to lay one more row of riser bricks, I'm sure I will get that done today eventually lol.

Update:
Today I learned about 5" duct, which I had previously never knew existed.   So I will buy 5 feet (or more) of the 5" stuff and I think it should fit very snug inside the mass.  So if everything's pans out with the 5" duct fitting inside the mass, I will have 5" duct going through the mass, and then a final 4" chimney stack after the mass.

If you have more wood in the firebox, there will be more burning at one time

I may agree if you build something like others that has been tested to what they designed, but my system is operating proof with video that it will only burn at the bottom until it collapses onto its self when you have a top loading rocket stove with a system sized access port at the bottom front for air flow. I have an out of balance wood chamber/magazine compared to "official" book and proclaimed specifications and it works amazing.


can i ask why you cant have a 5" smoke stack? why does it have to be 4"

I already have 4" double wall pipe for hvac or whatever, so that's what I was going to use.   5" would be great if I had some, or if I could find some affordably, but I'm not sure about that.   I think there is 5" stuff for pellet stoves out there, and I've seen 5" stainless stuff on "boat/marine heaters" like you see in some tiny homes.  

5" is very unknown to me, but I will likely be using 5" in the mass area for sure, as for the final stack, it will be 4" or possibly 5" if I can access anything adequate.

Two Questions:
1 :
I happen to have about 8 more firebrick remaining, I only need 6 for another riser stack/row.    Should I add another 9" stack/row?   My bell will be sitting on top of the firebox, or somewhere around that level. My bell will have a removable lid.  

2 :
I've attached a drawing to scale (1 block=1") to show my riser and bell size and outer diameters.   Should I exit flue gasses at the bottom of the bell at the rear of the riser? or bottom of the bell and side of the riser?   Or exit out the side of the bell? I prefer to exit the bottom of the bell...