Is my barrel to small?

Hi, I have a small place about 400 s.f that I want to heat with a rocket stove this winter. I found 55 gallon barrels but wanted something smaller to save on space. Then I found some barrels that the man said were 20 gallon barrels. They are 11 inches diameter. I build the firebox with firebrick and got a 6 inch stovepipe for the insulated vertical burn chamber. I put a piece of 8 inch duct around it and stuffed the space between it with insulation. I stacked two barrels on top of each other so the barrel is 42 inches high. I left the insulated stove pipe 1 1/2 inches below the top of the barrel and the 8 inch duct in the 11 inch barrel gives 1 1/2 inch of clearance all around. I am using 20 feet of 6 inch duct as the vertical flue. It doubles back and goes straight out the side wall. It does draw but not enough to pull all the smoke out of the house so it gets pretty smokey and some of the fire climbs up the feed tube also. Is the barrel to small to draw so do I need to use the 55 gallon barrels? Thanks for any advice.

I just read Rob Hills' forum question about the clerance between the barrel and the heat riser. He used brick for trhe heat riser and I am thinking since I have enough fire brick maybe I should use them for my riser and use the 55 gallon barrel. I have Ianto' book on rocket stoves. It seems like I will have to insulate around the brick riser with sheet metal and insulation to within 1 1/2 inch of the 55 gallon barrel. I think I have read other places that if you use firebrick for the riser you don't need insulaton around it since the brick is insulated enough. Any advice? This is the first rocket stove I have built so I am bumbeling my way through it.

Danny Zeigler : Please describe your fire brick and its sizes, I want you to paint me a picture not agree with me as to what is 'fire brick'.

The 1 1/2 '' gap is the gap between the top of your Heat Riser to the under side of the barrel, it is not Automagic-ly the distance between the outside of the Heat Riser and the inside of the barrel, tho it is close !

You need to read and understand the section dealing with the cross sectional Areas, C.S.A.s of your Rocket Stove, well enough to explain it to a 3rd party before you proceed !

If you had two identical Rocket stoves with two identical Heat Risers delivering the same hot exhaust gases to two different barrels, they both have the same job to do cool those hot exhaust gases.

Counter-intuitively the smaller barrel performs this by radiating the heat off of the smaller surface area of that barrel than the larger.

That is why when your three year old wants to be picked-up for a snuggle it feels so good, their little heat engines have a higher mass to surface area and radiate more heat !heat at a higher temp. relatively !

Come back here to this forum, and if needed we will talk you through it ! Pyro-matically yours , - Allen L.

Thanks Allen, I am not home right now, but I will post all the dimmensions later and try to put a picture on too.

one common bottleneck that causes a lot of problems: the junction where exhaust leaves the barrel. make it bigger than you think it needs to be.

OK, the feed tube and the opening to the riser are both 5” by 6”. The burn tunnel is 6” by 4”. The bricks are all 4” by 8 5/8” by 2 3/8”. I used three bricks on edge for the top of the burn tunnel which makes it 7” long. The riser is 6” black stove pipe surrounded with an 8” piece of duct. This allows for one inch of insulation. The barrels are 11” diameter and I stacked two so the total height is 42”. This leaves 1 ½” of space between the riser and the barrel and I left 1 ½” between the top of the riser and the top of the barrel. I cut a 6” hole in the bottom of the barrel an attached 6” duct for flue pipe. I have 20 ft. of flue pipe and then it goes outside.
Here are some pictures. I am using the concrete blocks since, believe it or not, I can’t find any clay. There is none on the property. I have called quarries, top soil and landscapers all with no success. So I plan to put one more course of block on and fill it with gravel. Then next spring I will see about finding clay.
When I fired the stove up it did work, but as I said in my original post the room got pretty smoky and I did have a little fire creep up the burn tube . Should I just go ahead and use my 55 gallon barrel and use the 20 gallon for the feed tube. Also If I use the 55 gallon barrel and make the riser out of firebrick do I need to insulate it? Any suggestions?
Thanks!

danny zeigler wrote:This leaves 1 ½” of space between the riser and the barrel and I left 1 ½” between the top of the riser and the top of the barrel. I cut a 6” hole in the bottom of the barrel an attached 6” duct for flue pipe. I have 20 ft. of flue pipe and then it goes outside.

Barrel is not too small in my opinion, but other details are not quite up to specs.
Two possible restrictions: the top gap is exactly right but I would give it 2" or more. Less is bad, more will work OK.

The second is the 6" hole in the side of the drum, this is a bit more complicated. There's a 1.5" side gap between drum and insulation canister and that's alright, but not at the spot around the exit. The smoke is coming from the top and partly from the side, so you are using about half of the circumference of the exit hole. In order to have enough space for the gas stream coming out, you have to widen this hole to at least 10", 12" would be perfectly adequate. Another remedy is to widen the side gap, in other words using a wider barrel and keep the 6" exit pipe.

danny zeigler wrote:When I fired the stove up it did work, but as I said in my original post the room got pretty smoky and I did have a little fire creep up the burn tube . Should I just go ahead and use my 55 gallon barrel and use the 20 gallon for the feed tube. Also If I use the 55 gallon barrel and make the riser out of firebrick do I need to insulate it?

You have to insulate the riser in order to maintain a large temperature difference between the inside of the riser and the outside between insulation canister and barrel. This so-called delta T is the drive of the stove. Stove pipe for the inside of the riser is bad, this will burn out in no time when the stove is running properly. Better to use a 55 gallon drum for the barrel and use a small drum for the insulation canister.

Then last but not least: you could leave out the stove pipe altogether and build the bench as a bell system. This is an enclosed space, feeding at floor level and exhausting at floor level. The inside of the bench is very much wider compared to the feed hole, so the gas velocity will slow down a lot. Because the hot gases are lighter, they will rise to the top, driving the colder gases to floor level and out. You have to use more blocks, also at the wall side, and make it virtually airtight all around. The top plate can be made out of concrete pavers, two layers thick and the seams not directly above each other. It doesn't matter that the feed and exhaust are close to each other, the bench will get hot right to the end.

Just a proposition, the western world is not used to constructions like that because these are invented by a Russian professor in around 1910.

Thank you Peter you gave me some ideas for my own creation.

O.K, yesterday I reworked the rocket stove. I used a hvac boot to connect the barrel to the flue. This allowed me to cut a much bigger opening in the barrel. i also changed the exit form two 90 degree turns to two at about 45 degrees and put a cleanout after them. This can be seen in the pictures. The stove still doesn not draw well at all. Smoke poured back and out the feed tube. I even shoved the fire into the burn tunnel and the fire would rocket back in the feed tube. Maybe I need to just go ahead and use the 55 gallon barrel. I could cut the 20 gallon barrel and existing 6 inch riser off and leave it and cover it with the 55 gallon barrel. I guess I would have to get a piece of sheet metal to wrap the 20 gallon barrel in to insulate it and leave about 1 1/2 inch between the new sheet metal riser and the 55 gallon barrel. Any other suggestions.

Danny Z : How are you sealing the two barrels together ? Do you ever get smoke out there ? How does the stove pipe end after you send them out through your homemade triple wall ?

Before I gave up on the small barrels i would undo the barrels remove the 3 bricks laying on their side and replace them with 2 laying flat AFTER you raise the height of your burn tunnel
so that the two bricks laying on their side are raised up to meet the bottom of the lower Barrel. You have a burn tunnel that is about 2/3rds of the other C.S.A.s . For TRAIL ONLY I would
allow the use of pieces of sheet rock /cob laying down where the' three bricks that made the top of the burn tunnel ' are replaced with '2 bricks that make up the top of the Burn tunnel.
Again the reason for doing this is for a temporary test raise the height of your Burn Tunnel to see if this is the further cause of your stoppage !!

I keep repeating that you will need an air gap between your cob bench and the Sheet Rock wall and I cant stress strongly enough that will you can continue to experiment to find your
stoppage this must be committed to before you try to use it for the purpose you are building it for ! Be Safe Allen l.

If laying the bricks sideways end up giving you an increase of a 1/2'' at the bottom of the Heat Riser I would call that a good thing ! A.L.

Hi Danny: A few suggestions, but first, as Allen has stated-- and couldn't be more important: safety!

By looking at your pictures, I can see that you have two critical issues that need to be addressed before you go any further:

1) Are you building this on top of a carpeted floor?!?!?!? It looks as if you are using insboard or ceramic fiberboard under the construction, no? This may protect you enough not to start a fire on the underside of your floor, but you are going to cause some damage to your carpet. Granted, you may not have old hardwoods underneath to justify removing the carpet entirely, but why not at least razor it out from under the RMH?

2) Unless you plan on placing a very impressive heat shield in between the barrel and the wall, you are WAY too close to the wall-- especially if you are still considering switching to the 55gal barrel.

Unfortunately, to properly rectify these two issues and when considering Allen's point made about your bench clearance to the wall , you are looking at tearing down and starting over-- which would be fine, because your draw issue can then be addressed as well:

Simply put: the CSAs of you feed tube and beginning of your heat riser are larger than your exhaust. 5"x6"=30"sq ; 6" dia. duct= 28.26. Yes it is larger than your burn tunnel CSA, but in the long haul through your bench that's choking things down.

I think you have a great system in the making, but I also think it is critical that you tackle the safety concerns before moving on.

Keep at it!

Allen,
I cut the ends of the barrels out and they fit together very tightly. I put some of the heat resistant calking that is used for wood stoves around before I tapped them together with a hammer and a 2 by 4. No smoke comes out and it would probably be hard to get them apart again. Right now on the outside the house I just have the 6” flue pipe stubbed out. I also tried putting an elbow on it which I angled down at about 45% angle to see if it would help draw.
I didn’t quite follow you on laying the bricks on their side. Do you mean to raise the height of my burn tunnel 2” by laying bricks flat under the three on their side that I am using for the roof of the burn tunnel?
danny

danny zeigler wrote:Right now on the outside the house I just have the 6” flue pipe stubbed out.

Hey, wait a minute! Are you implying your exhaust is like a laundry dryer exit? When this is the case, this won't work at all, especially when your dwelling is more than one storey high. My advice: place some lenghts of stove pipe on it to at least the highest point of the roof, preferably a bit higher. When this make-shift chimney could be insulated as well, that would make all the difference in the world.

Right now Peter I have 6" round duct stubbed outside through a tripple wall sheet metal duct. I am just putting everything together and tring to get the stove to draw. The stove is on the first floor and the flue runs horizontally through the bench and then exits the house just above floor level. Are you saying that I have to build a vertical stack on the outside of the house up to the roof like with a wood stove?

Chris, the floor is a concrete slab and a portion of the wall is concrete as well. about 7 feet is studs and drwyall so I will have to make an insulated air gap between the flue- barrell and the sheet rock. If I use the 55 gallon barrell I will probably,as you said, have to start all over. Oh well.

danny zeigler wrote:Are you saying that I have to build a vertical stack on the outside of the house up to the roof like with a wood stove?

Yes that's the picture. Read this artcle about the neutral pressure plain and other relatively unknown phenomenons. Especially the part after the header "Is Your House a Better Chimney Than Your Chimney?" That might be the problem in your situation.

OK, first I disconnected the flue from the barrel and lit up the feed tube with leaves to see if the stove was drawing. I did get a sideways burn, the top of the barrel got warm and smoke came out where the flue would hook up to the barrel. Then I hooked up the flue pipes and sealed them up. I built a fire and got a sideways burn but also smoke coming back up the burn tunnel. I had the fire going for about a half an hour. There was smoke coming out the flue on the outside of the house and there was a sideways burn most of the time although I would get fire creep up the feed tube at times and smoke also came up the feed tube. Twice in the 30 minutes I had to open the doors and window since it was getting too smoky in the room. I think I have concluded that the 20 gallon barrel, while it does draw, does not have a powerful enough draw to suck all the fire and smoke horizontally. So I have decided to use the 55 gallon barrel.

This is what I am thinking now; I would like to cut off the 20 gallon barrel and cover it with the 55 gallon barrel. If I leave a space of 1 to 1 ½” inch between the 20 gallon barrel and the 55 galon barrel and let the 55 gallon barrel hang out into the room away from the wall I will have about 10 inches between the 55 and the sheetrock exterior wall. I am sure I can build an insulated heat shield to protect the wall . I can take a piece of corrugated tin and wrap the riser inside the 55 so that it is within 1 ½ “ from the inside of the 55. This would mean, however, that the flue pipe would not come up in the middle of the 55. I don’t see how this would hurt the performance even though the heat riser will hit the top of the 55 away from the center. I guess I will just have to heat my tea on the back of the barrel.

Of course since this is my first rocket stove this is just my guess. I would appreciate any suggestions before I go tearing this one apart.
Thank you,
danny

One other thought I had which I probably know what the answer will be. If I do what I described above would I absolutely have to put the larger insulation around the 20 gallon barrell inside the 55? It would be nice if I could just insulate inside the 20 and then put the 55 over it. Would the force of the heat in the riser push the volume out of the 55? Just a thought.

Danny, what you are describing is my favorite way to build the riser. No need to enlarge the small barrel.

Thanks Matt, That makes me feel beter. I am going to do the 55 gallon barrell this weekend. I will keep you posted as to how it works.

Well, I made the change to the 55 gallon barrel. When I fired it up but was really bummed to see that it didn’t draw any better than the 20 gallon did and the smoke really came back up the feed tube. I left the 20 gallon barrel and put vermiculite inside it. I have 1 ½” between the top of the riser and the top of the barrel. I am doing something wrong but don’t know what it is. Here are some pictures if anyone has suggestions.

Try to widen the top gap first.
When this won't work check everything, even when you think it should be allright. Like side gap, transition from barrel to bench etc., untill you reach the chimney part. My guess is: do a proper chimney, dryer vent exhausts won't work in a normal house, only in a one-storey hut featuring an airtight roof. Check the bathroom ventilator or vent channel, kitchen range, fireplace or whatever you have there. I could see a paneled door in one of the pictures, is it in a house of about 1930? Maybe it's not you doing something wrong, maybe it's something inside the house.

Hello everyone,
The structure the stove is in is an 18 year old barn that was converted to a yoga studio and then to living space. It is a gambrel roof which is the typical two pitch barn style roof. The flue goes out on what would be the gambrel roof end. It is a two story and the second story is in what would be in the barn roof. It is well insulated and it has always been heated it with portable electric heaters. The door in the picture is an exterior door. I do not want to and really cannot run a flue pipe up above the roof. There is a double door above the flue off the second story and I would also have to run the flue through the soffit overhang.


The flue is sealed up and the opening from the barrel to the flue is wide open. When I fired the stove up the smoke did exit the flue to the outside and the barrel got warm but a lot of smoke came back up the feed tube which makes it impossible to use the stove without getting smoked out.


Here is my thought about running the flue above the roof. The flue gas has lost most of its heat by the time it exits the flue outside the house. It has been pushed along by the force created in the riser. If the force is not great enough to push it out the horizontal flue it certainly is not going to be strong enough to push the warm and rapidly cooling flue gas another 20 plus feet vertically. In all the rocket stove u-tube videos I have seen I don’t think any of them exhausted above the roof. I guess I could at least try hooking on a vertical 6 foot flue pipe on to where the flue exits the home to see if that works. That would be easy enough.

The only other thing I can think of that would cause the problem is that the 20 gallon riser is on the side of the 55 gallon barrel and doesn’t come up in the middle of the barrel. This is because I tried to use a 20 gallon barrel first and built the firebox assembly for it. It also doesn’t have enough insulation to nearly fill the 55 gallon barrel. There is a larger volume of air in the 55 gallon barrel so the volume of the cross section area is not uniform at this point.

To remedy this I will have to move the entire firebox over and start again on the feed tube and barrel assembly. I guess I will try that but it will be my last attempt and if that doesn’t work I am going to take it all out and glue the carpet back down.

Thank you everyone for all the advice. I hope I can get it working right since I am getting tired of messing with it. Maybe if nothing else my rocket stove experiments can be used as an example of how not to build a rocket stove.

danny zeigler wrote:If the force is not great enough to push it out the horizontal flue it certainly is not going to be strong enough to push the warm and rapidly cooling flue gas another 20 plus feet vertically.

Go ahead, it's your stove and your house. In my humble opinion, you are trying to find a mare's nest, there's no easy way out.

It is pretty clear in your photos that your transition CSA from your barrel exit chamber to your horizontal duct is mudded up much smaller than it should be. This opening should have the same CSA as your duct through your bench.

Take some of your pink insulation out, light up some incense. If the incense smoke it pulled out of the house then your build is wrong on the inside. If the incense smoke is pushed back inside then you need some kind of external chimney.

In all the rocket stove u-tube videos I have seen I don’t think any of them exhausted above the roof. I guess I could at least try hooking on a vertical 6 foot flue pipe on to where the flue exits the home to see if that works. That would be easy enough.

I had the SAME EXACT problem as you, for me the solution was hooking it up to an external chimney and all my problems went away. I had outside positive pressure fighting RHM positive pressure.

See my pics My build

Daniel and Peter, I will try putting a flue pipe extension on the outside of the house. That will be the easiest next attempt to get the stove working. There is a slight breeze outside and I do have some air blowing back up through my feed tube so I hope an extension will help although I don't see how I can run it up above the roof.

Chris, you said the transition CSA from the barrel to the exit chamber of the horizontal duct is mudded up smaller than it should be. Actually the firebrick transition from the barrell to the 6 inch duct is larger than the 6 inch duct. In the picture it looks like the 6 inch duct is partially mudded shut. There appears to be some clay on the inside of the duct but that is just a thin film of clay that was left after I wiped it off with a wet rag. The duct is completely open.

Wow, what a lot of work, trial and error and then, nothing! How is it doing now, Danny?

I have the same question: is my barrel too small?

I am also building my first rocket stove, to heat a small cob greenhouse adjacent to a small chicken house. I have assembled most of my materials, and pulled up the floor and am getting close to having a configuration I think will work. I am planning to use a 14 inch diameter barrel to house the 6 inch heat riser (with 2 inches of insulation, yielding 2 inches of clearance between the heat riser and the barrel wall, and I was planning to leave 2 inches between the top of the heat riser and the barrel ).

Another thing that is really puzzling me now is is the place where the gasses leave the barrel and go into the ducts that will be housed in mass.... I saw that Danny said he used a hvac boot. I googled to see what that is, and now my question is do they make those out of non galvanized steel? I thought galvanized off gassed at rocket stove temperatures. It sure would make things easy if I could get something like that.

I guess that makes two questions, the barrel and the transition into the heating ducts.

Thanks

Thekla

This problem you're having Danny is the same EXACT problem that we're having right now with ours. The barrel size doesn't matter, it seems...because we've tried various things with them. The gap at the top of ours (between the outer barrel and the riser) is about 4.5 inches tall.

Smoke. Smoke. Smoke.

Near to no draw.

We got frustrated and ripped the flue off the outer barrel and lit her up - HOT.

Considering that it's about -20 degrees F outside right now - and that we had to open the door to let the smoke out...there is "something" coming out of the flue area...but we're not sure if it's pure steam or smoke because it has a weird smell to it that isn't quite smoke, and isn't quite steam.

I had hoped you wouldn't have stopped responding...because had a solution been met - other people could have benefited. I am frustrated right now and trying to work through the problem solving process.

This thread has, however, been highly useful and I think it should be pinned...to be honest lol.