Heater problems in a 200 Sq Ft camp. Your input is desired.

[aefriot]

Hello,



I am building a 1000 Sq Ft round square bale house next year. I wanted to build a prototype cook stove and heater in my camp to be sure I built the heater correctly in my house. It's a good thing I did too because it looks like it's going to make more of a mess to fix it than I made to build it. I wanted something that would retain heat well and something that could be cooked on. So I mashed up a sidewinder batch box ( Peter Van Den Berg @ batchrocket.eu/en/designs#core6) and the tiny masonry stove (https://walkerstoves.com/tiny-masonry-cook-stove-plans.html).



I know I have made errors somewhere as I am not getting temperatures that are hot enough in the fire box and in the riser. I hope others can help me to correct my mistakes and make this a working stove/heater.



Currently, the main purpose of this appliance is to heat. I plan to have two firings per day to coincide with two meal times (Breakfast and dinner) so to heat the cooking surface. Secondary is to cook meals.



Troubles:

Right off the bat, smoke showed me the many holes between bricks that were not properly mortared. Holes in the outer skin, holes in the insulation seams and leaks in the door gaskets. PATCHED!

Doesn't appear to burn well. Doesn't burn hot enough to burn cleanly. It always smokes. I can open or close primary air (1 1/4" x 5 3/4") and it doesn't make much difference on the amount of smoke, except to put out the fire if I close it too far.

Cook top will not get hot enough to cook.

The interior of the heater smells of creosote.

Moisture is condensing inside the flue and dripping on the floor, stove or in pans placed to catch the condensate.



After a full burn, the maximum temperatures I could read are on the sketchup rendered image of the heater. I cannot upload right now so I will describe them.

320F at top of external firebrick skin of riser left and front sides

230F at bottom of external firebrick skin of riser left and front sides

240F on cook top nearest riser

180F on cook top furthest from riser

450F in oven on fire box side

250F in oven opposite fire box

125F at flue elbow at side of heater

110F at second flue elbow

75F at natural stone skin on left (2nd skin) and right (single skin) of heater near flue exit

70F at natural stone skin (2nd skin) at back of heater



I will give actual measurements of stove and not the Sketchup measurements.



Parts of heater:



Foundation

48" L x 36" W x 4" H pad on ground level

Layer of 8" D x 8" H x 16" L concrete blocks

2 layers of 8" x 4" x 16" L concrete cap blocks

1 layer of standard brick laid flat

1 layer of full size fire brick laid on edge every other row (skip row)



Fire Box

The fire box is 21 1/2" D x 14 1/2" H x 9" W. Double skin back with firebrick inner and 4-5" natural stone. Single skin between oven, riser and bell 2. Top is double half brick thickness. Bottom is 1 and 1/2 fire brick thickness.



Venturi

The venturi (including the venturi pipe port) from the base of the riser to the top of the venturi is 2" W x 2 5/16" D (full brick width) x 12 1/4" H. My venturi pipe does not reach up into the middle of the venturi between the fire box and the riser, but is a flat piece of 1/4" plate atop the 45 degree cut brick to the middle of the venturi. From the top of the venturi pipe opening to the top of the venturi is 6 1/2". I did not install a pipe/tube from along the fire box floor to the venturi since there is a tunnel made by the brick and it gave me the opportunity to just drop in different venturi pipe types and openings.



Riser

The riser interior is single half fire brick inner 6 5/8" x 6 5/8" square x 47" to the cover. It does have angled fire brick opposite the venturi opening to aid the gasses upward. The opening above the riser is on the front and left side and is 3" tall. The passage for the gasses to go down is "L" shaped and 3" D x 12" W x 29" H. Externally, the riser is insulated by 1" ceramic fiber board on all four sides and 1/2" ceramic fiber board on the top under the riser cap. The front and left of the riser are the only sides that the gasses flow. where the gasses flow down and are redirected under the cook surface. currently, the external half brick brick skin on the riser are not insulated. I wanted to be sure the gasses would cool enough to "pull" gasses up the riser.



Cook top

23 1/2" x 24 3/4" x 1/4" plate steel (not insulated)



Oven (Bell 1)

21 1/2" D x 23" H x 14 1/4" W with 1/2" ceramic fiber on 15 1/2" W x 18 1/4" H door. Double skin left and back. Fire brick inner and 3-4" natural stone outer Metal front with 1/2 ceramic board insulation. Single skin firebrick wall between oven and fire box



Bell 2

25" H x 25" D x 2" L Single skin 3" natural stone.



Exhaust

The exhaust is 6" out with non-insulated pipe. A 90 up, 4' to a 90 to horizontal 3 feet with a 90 up to a cap at 5 feet (with three feet above the sheet metal roof and 2 feet above the peak).



I have tried uploading images and Sketchup file but the forum has reached its limit on file uploads. Please email me for the images and sketchup file.



The Sketchup file is not exact, but I believe it's close to what I have currently working in the camp. I do not show the front of the stove, but left it off for ease of viewing (and I'm a hurry right now). The left is for the black oven, the center is the fire box and the right side is for the possibility for a future small quick-fire rocket heater for those times when I just want to heat coffee or make lunch.

[Dan (Upstate NY, USA)]

Put some photos on a sharing site and put the link here. You can write all this but when we see photos of the build then someone will be like "Ah there's the problem"

[peterberg]

Hi aefriot, welcome to the boards.
Most of the configuration you have there isn't clear to me. Is it my batch box rocket design or is it Matt Walker's riserless core? No clue what you mean by venturi pipe, and I understand the secondary air provision isn't up to specs of neither mine or Matt's recommendations.

One possible snag that stands out: 3" space above the riser (commonly called the top gap) on front and left side. Assuming you are operating a 6" system, that would be half the bare minimum for J-tubes and 1/4 of the tried minimum for batch boxes. Although I wouldn't go for less than 1' myself if I can find the space for it.

In short: the top gap should be all around the riser, and preferably twice as high. In case this isn't possible because of heater wall constraints there's no alternative than to rebuild the thing.

Since there is apparently such a severe restriction in your build, I expect there would be more pinched spots like that.

Pictures would help immensely, same goes for a correct skp file.

[aefriot]

I am currently out of town. I will set up photo sharing when I get back. I should have thought of that earlier when I could not upload photos and the sketch file.

[aefriot]

Here are some images to show you what it currently looks like.

Rear left corner



Front right corner



Front




Sketchup file to see what insides look like.

Oct 25, 2018 11:46:22 GMT -8 peterberg said:

Hi aefriot, welcome to the boards.

Most of the configuration you have there isn't clear to me. Is it my batch box rocket design or is it Matt Walker's riserless core? No clue what you mean by venturi pipe, and I understand the secondary air provision isn't up to specs of neither mine or Matt's recommendations.

I attempted to make a stove like Matt's, but with another area of mass above the cooking area for the ability to radiate heat over lower cabinets to regions beyond the kitchen area directly rather than using the intermediary cabinets to relay heat.

What I'm calling a venturi is the secondary air pipe/tube. 

Oct 25, 2018 11:46:22 GMT -8 peterberg said:

One possible snag that stands out: 3" space above the riser (commonly called the top gap) on front and left side. Assuming you are operating a 6" system, that would be half the bare minimum for J-tubes and 1/4 of the tried minimum for batch boxes. Although I wouldn't go for less than 1' myself if I can find the space for it.

In short: the top gap should be all around the riser, and preferably twice as high. In case this isn't possible because of heater wall constraints there's no alternative than to rebuild the thing.

I believe you are right. When designing the thing I tried to keep ample room for gasses to move. Looking back, I see I must have had math errors which led me to too narrow of a passage above the riser. I am going to take a look at it today to see if there is a way to ensure there is enough flow to allow combustion to breathe.

[Dan (Upstate NY, USA)]

link
If this worked then the Cyan color is your restriction.... I think...

[Dan (Upstate NY, USA)]

Ha Ha figured it out

[aefriot]

I understand that it is customary to build an area around the riser for the exhaust to flow. Believing if I have an area large enough to flow the gasses, I could use less space or fewer sides of the riser. I wanted to use 2 sides, the front and the left which would be closest to the flat steel cook surface.

The riser is 6 1/2" square. 6.5 x 6.5 x 1.5 = 63.375. I'll round up to 64 sq in. CSA for the remainder of the exhaust's journey through the stove to the flue.

I have started to tear down and measure CSA according to how rocket stoves operate and found 3 issues with my design which I am embarrassed to say should never have been built into the stove. And use to be good at math.  Hopefully, others can learn from my mistakes.

First, my clearances above the riser were too small.

The path out of the riser to the front and left side measured 8" x 3" each giving me a total of only 48 sq in total instead of the 64 sq in. required. At a minimum, 64 / (8 + 8) = 4, this "top gap" (thank you Peter) should have been 4 inches tall to maintain the 150% of CSA of riser, not the 3 inches I built into the stove. I believe that since there is a change in direction, there needs to be extra room for the gases to smoothly make this change. I think i can easily make the "top gap" 10 inches.

Second, the clearances under the part that the exhaust goes down the outside of the riser were 2 inches. 2 inches x ~21 inches (roughly the depth of the stove) is only 42 sq inches. much less than the 150% of the riser CSA.  Clearly not large enough. The new clearance is 4 inches. 4 x 21 = 84 sq in. This should flow enough exhaust gas.

Third, the total CSA of the "tunnels" under the fire box is not 150% of riser CSA. The five tunnels are each the size the end of a full size brick (2 1/4" x 4 1/2").

2.25" x 4.5" x 5 = 50.625 sq in.


This is harder to overcome. I see no easy way to change these numbers. All I needed to do with the other bottlenecks was to remove the bricks, insulation and support member for the riser turnaround then raise the support and reassemble the bricks and insulation. Just a days work. To increase the CSA of the tunnels under the fire box would take three days to disassemble and reassemble with larger spaces. Possibly, I could break apart the softer brick under the parallel bricks to increase the area for exhaust gas flow. For now, I will just try it as it is. It's an experiment. Maybe you all can see an alternative to the methods I have thought of to correct the CSA of the tunnels.

I am going to retry tomorrow after my adjustments.

[satamax]

Well, i see several restrictions.

Obviously the full bricks under the firebox are one. To explain, in fluid mechanics, there is something called the boundary layer. Basically, the fluid sticks to the wall it is passing by. In a channel, effect of drag, in uncompressed air is affecting up to three cm away from the wall. that with two side walls between your bricks, you have the thickness between the bricks acting as a "plug" well, just a partial one. but i'm pretty sure it's a drag on gases. What i would do in this case, is try hard to remove those bricks one by one, and replace these by splits.

This would give you more room.

And there is one thing i don't like at all



When i measure with sketchup, i get 2-1/16 so multiplied by the circumference of the 6 inch hole, i get 38.87sqin of gap. But it is even less than this, since the pipe is nearly next to the back wall.

My advice would be to relocate the pipe to the bottom front, where your tunnels bellow the firebox exit.

Actually, where they exit bellow the heat riser is a restriction as well. You have two channels which are completely free, and three chocked by the four inch space between these and the wall, further chocked by the heat riser insulation.

[aefriot]

Oct 28, 2018 0:21:33 GMT -8 satamax said:

Well, i see several restrictions.

Obviously the full bricks under the firebox are one. To explain, in fluid mechanics, there is something called the boundary layer. Basically, the fluid sticks to the wall it is passing by. In a channel, effect of drag, in uncompressed air is affecting up to three cm away from the wall. that with two side walls between your bricks, you have the thickness between the bricks acting as a "plug" well, just a partial one. but i'm pretty sure it's a drag on gases. What i would do in this case, is try hard to remove those bricks one by one, and replace these by splits.

This would give you more room.

You are right! I made that error knowing darn well that the surfaces will drag on the passing gasses. I forgot about friction. Since the moving gasses cannot move the bricks, the gasses must slow down. It's going to be hard, but I'm going to have to try to remove the full bricks and replace them with half bricks. Just how do I slide the bricks out from under the fire box? I don't! I am going to tear it down and start over with adjustments. I just need a few days to take care of a few things outside before the snow comes to stay and covers everything until March.

Oct 28, 2018 0:21:33 GMT -8 satamax said:

And there is one thing i don't like at all

When i measure with sketchup, i get 2-1/16 so multiplied by the circumference of the 6 inch hole, i get 38.87sqin of gap. But it is even less than this, since the pipe is nearly next to the back wall.

My advice would be to relocate the pipe to the bottom front, where your tunnels bellow the firebox exit.

Actually, where they exit bellow the heat riser is a restriction as well. You have two channels which are completely free, and three chocked by the four inch space between these and the wall, further chocked by the heat riser insulation.

I see this as a very big problem as well. My design changed once I found my foundation had to be smaller than I had originally planned. I could not cut out another floor joist for the additional room so the stove length sacrificed. Looking back, I could have made the skin bulbous and give more room to flow but I didn't.

There are too many issues with my stove! But you know what? I have three, possibly four, other stoves to build in various buildings. This, being my first, was a valuable lesson in stove building. Now, I can think ahead to solve potential or reduce the number of assembly, design, work flow and gas flow issues and reduce frustrations and work load. I look forward to seeing what the new revision will be like. Thank you all for your contributions.

[satamax]

Aefriot, i feel for you, it's snowflaking today at my place, and i beg for it to stay away until i have all roof work done. One skylight, two sets of snow stops, two gutters.

For replacing your bricks, try to find something like this



You don't need much wiggle play. Guitar bridge jacks could be of the right length.

And, as i said before. Take your black stove pipe down to the bottom front of your stove, put a 15 or 22° elbow, where you have the elbow now.

Put a 2ft or 20 inch length of black stove pipe down to the front, and then another 90° entering the stove. This is nearly nothing to doGoing through your pebbles should be easy enough, and your "bell effect" will be better.

[satamax]

Another solution two wedges and a hammer.

[aefriot]

I am still debating what I'm going to do. Modify or replace? I have too many other projects to take the time to replace so repairing looks like the option we are going with. I can try to remove two rows of the full bricks and replace them with steel supports under the fire box. This could increase the CSA to 60 from 49 sq in which would be a big boost to flow. I can also add another 6 in flue to the front of the right side to increase flow there as well. If I still do not feel the stove is living up to it's potential, I can replace remaining full bricks under the fire box with half bricks increasing CSA under the fire box to 73 sq in. If the bricks change easily enough, perhaps I will do them all at once. I fear breaking the fire box into pieces.

[aefriot]

It took less time than I thought it would to replace the full fire brick under the fire box rows (from the front) 2,3 and 4. I used 24" and 13", 1 1/2" x 4 3/8" hardwood diagonal cut into wedges driven under the fire box to raise it enough to pull out the full blocks. I had a piece of 12" I-beam so I cut three 4 1/2" "T"s with a jig saw. A torch would have been faster, but I couldn't be sure of getting a smooth and true 4 1/2" height without over-sizing it and grinding it down to size. That would take far too long. My mortar did break in many places, but I can repair that to be sure it maintains air-tight as possible. I'm waiting for the mortar to dry on my outer skin so I can install the second exhaust flue and tee it into the first flue to share the exit out the roof.



Updated Sketchup file

[aefriot]

I had a fire today. I'm believing it was better than before replacing the full brick under the fire box and adding a second 6" (152mm) flue exit. I have much less condensation. External flue temperatures rose fairly quickly and maxed at 125*F (52*C). I'm believing the stove condensed because the mass was cold when starting the fire and hasn't warmed through. I am a bit disappointed that my cook top didn't attain a cooking temperature. After an hour burn the steel plate was at 250*F (121*C) . I'm wondering if my primary air is too small.

Riser internal dimension is 6.5" x 6.5" (165 mm x 165 mm) = 42.25 in2 (27,225 mm2) Primary air is 5.75" x 1.25" (146 mm x 32 mm) = 7.2 in2 (4,672 mm2)/42.25 in2 (27,225 mm2) = .17. Primary air is 17% of riser CSA. I believe that is a bit low. I could open the opening easily enough to attain the proper mix, but I was thinking I might be able to insulate the inside of the riser with 1/2" (13 mm) ceramic fiber board. This would reduce riser CSA to 5.5" x 5.5" (140 mm x 140 mm) = 30.25 in2 (19,600 mm2). 7.2 in2/30.25 in2 = .24. The primary air percentage would rise to 24% of CSA of the riser and the temperatures might go higher and increase the cook top temperatures by 100*F (38*C).

I'm going try to log temperatures before making any changes. Maybe someone can chime in who has experience with these heaters. At least you all can see how this stove performs. I hope it will be useful to others. I know I haven't found actual numbers as to the temperatures produced for finished products, only cores and while interesting, gave me no real world data for finished products.

Two hours after the first burn from 55*F (13*C) cold mass.

November 3, 2018, 22:15

Temperatures are as follows:

Item	F	C
Reference post (building temperature)	80	27
Outside temperature	37	3
Top of riser skin	222	106
Bottom of riser skin	220	104
Right cook top	228	109
Left cook top	140	60
Left side of heater (Double skin)  2.25" (114 mm) fire brick double thickness cardboard 3.5" (89 mm) natural stone	82	28
Left side oven	250	121
Middle of oven	300	149
Bottom of oven	160	71
Right oven side/Left side of fire box	396	202
Right side of fire box	412	211
Right side of heater (Single skin) 3" (76 mm) natural stone	100	38
Back of heater behind fire box (Double skin) 2.25" (114 mm) fire brick 1" (25 mm) air space double thickness cardboard 5" (127 mm) natural stone	92	33