David Searles

why would I want to send 150 degrees up the chimney when I can send 70 degrees up? 150 degrees would hold a heck of a lot more moisture and that combined with the warmer air would rot the clay brick in the 4 story tall chimney even faster. By cooling the exhaust down to 70 it precipitates out some of the moisture, which drips out of the exhaust pipe into a bucket placed in the basement to catch it.

I had thought that 5" pipe was going to be too small, but as I said, draft was never really a problem. I might have been able to go down to 4, but there wasn't any reason to try to go smaller as I had plenty of clearance for 5". I am thinking that by getting a liner that it will increase the draft (but we'll see) It's a pretty open space, and I get a pretty good discount at the hardware store so I can afford to experiment with different sizes of flu pipes. I love to tinker. I might go crazy and build a cylindrical masonry support wall to support the upside barrel upside on without any cuts in the sides of the barrel for the entrance tunnel or the exhaust. I thought I would incorporate openings for them into the cylindrical wall, which would now allow me to go three of 4 courses higher with the heat riser. But that said - I think that the present barrel with the hole for the exhaust and the rectangle cut out for the input tunnel would be plenty strong enough to support another 500 pounds. But if I think that there is a problem I could fill it only half way or so and still get an incredible amount of thermal mass until I bolted together a bracket to hold the 2nd barre up independently. Thank you for your concern though.

except in this case the exhaust going into the the chimney while the fire in the unit is blazing, is about 70 degrees f of really moist air. Over not too much time that warm moist air will disintegrate the clay in the chimney brick from the bottom up. This is the same reason it is a terrible idea to vent a really efficient gas fired water heater into a brick chimney without a stainless steel, or at least an aluminum liner. The exhaust simply isn't hot enough to heat the bricks enough for them to dry themselves out from the stored heat between firings. As a precaution for this year I am disconnecting the flu pipe going to the chimney and allowing the chimney to free vent through the summer. That will dry the bricks out somewhat from being exposed to the moist air from the stove all winter long.

as you may recall, I built the core of my rocket stove with diagonally sawn laid up courses of soft file brick. It formed a, octagon 5.5 inches across the height of a 55 gal steel drum. I tried venting it out the side wall, but the wind kept causing blow back. I tried putting a whirley bird vent on the exhaust. That helped slightly, but still at all reliable. I have a 10" exhaust pip that comes out the side of the barrel at the bottom with a 10 " pipe. This serves as a plenum, and then I reduced it in stages down to 5" and ran the pipe through a hole for a hot air vent down into the basement to the brick chimney that used to be for the oil furnace. (Never mix fuels in the same chimney) I got all the draft that I ever needed, and in fact had to put both a barometric damper and a conventional damper to control the draft. This worked perfect, except for a few relatively warm days with low barometric pressure and little or no wind. On sever occasions I was able to remedy the problem by going down into the basement and putting some lit news parer into the chimney to jump start the draft. On A few days, even that wouldn't work, but as they came on relatively warm days, it wasn't a major problem. Some days, when the weather conditioner were just right I could easily exceed 900 degrees F at the top of the barrel.

I have decided to change a couple of things.

#1 I hadn't realized that it is a really bad idea to be sending warm moist exhaust up a clay brick chimney. That gentle white condensation at the top of the chimney is very nice - except, that there is not enough heat going up the chimney to dry out the moisture. It wouldn't take too many seasons of this to completely soak the clay bricks and induce a mechanical failure because of the weight of the bricks stacked on top of one another. So I must get a stainless steel liner.

#2. the 5.5 dia. heat riser is OK as a parlor heater, but not to provide the main heat for the whole house in Rutland Vermont. I'm going to take out the 5.5 inch dia. set up and rebuild it into about an 8" setup, 3 or 4 courses higher, again with soft fire bricks cut on an angle. With this set up I will be able to burn much larger pieces of wood. I about wore out my shoulders spitting wood down to kindling wood size to be able to fit it in the burn chamber. I'm thinking with a larger diameter heat riser it will also give it enough umph that it seems to need sometimes to overcome the conditions above that on some days caused problems. Likely I will have to increase the run the the chimney with 6" pipe, but we will see .



#3 I am gong to try an experiment with placing a 55 gallon drum filled with water directly on top of the upside down barrel that covers the heat riser. This will weigh about 400 pounds and will give as much thermal mass as 800 pounds of stone, and will be taking heat from the hottest part of the unit (the top of the barrel) (Of couse this will have an open vent at the top to prevent pressure buildup, and I will add more bracing underneath the stove down in the basement.)

Dried bio mass per pound all essentially contain the same number of BTUs. It's a heck of a lot quicker to air dry bamboo however. The University of Vermont study was on a per acre basis, I should have mentioned that. The trees will provide a full canopy, with relatively only a small amount of light making it to the ground , soaking up a maximum of sunlight where bamboo cannot do that as effectively - or so it seems.

The University of Vermont did a study as to the best tree to grow for bio mass energy - to identify specifically which tree most efficiency converts sunlight into BTUs to be released by burning. The tree that best did that they found was fast growing Poplar trees.

As to the galvanized question. I am not absolutely sure, but as far as I can tell, there is black stove pipe and galvanized, unless you go to stainless. one way to test is to scratch it with a knife and then put a soaking wet wash cloth soaked in salt water. Within a day if you see rust start to form only at the part where you scratched it, it is definitely galvanized. But after my first week of burning, in my particular unit - I would say that only the first piece of duct off of the bell needs to be treated. But it is really easy to do in a 5 gallon bucket, even if you soak one end for two or three house and then the other. I had originally said that I started off of the barrel with 12".. I was wrtong. I started with a 10 to 8 reducer, a short piece of 8, then a 8 inch tee with a clean out, then a 8 to 7 reducer, and then a 7 to 6 reducer.

it seems like a whole lot of well intentioned technical mumbo jumbo.

I am using a heat riser with 4.5 inches of soft fire brick for its walls.

As I write this my first build stove with the soft fire brick is putting out a constant 580 degrees F at the top of the barrel, with no vertical chimney vent, and this when it is 50 degrees outside and it is raining, so there is plenty of moisture in the intake air that has to be burned off.

why would I go through the trouble of lining the heat riser with 1" of hard fire brick? Especially when the soft fire brick so easily lends itself to building the heat riser into a self supporting stable octagon design which seems to be far far more conducive to a hot burn than a rectangular system?

I found out very quickly that with a horizontal pipe extending from the rocket stove to the outside of the house, that even a slight gust of wind will blow even a little exhaust back into the fire and put it out immediately. This seems to be so because the exhaust gas once it leaves the heat riser is so depleted of oxygen because of such an efficient burn, that it simply will not sustain fire. This became very clear to me when I was trying to re-energize the draft a little bit by putting a propane torch slightly into the fire tunnel, and as soon as the slightest bit of gust hit the side of the house, the slight amount of exhaust blowback put the flame of the torch right out.

I got an 8" " whirly bird" vent from Lomanco, I put a tee in the 6" horizontal stove pie and adapted the 6" to 8" on the top of the tee and put the vent on top of that, (I used a tee, so that I could put a cap on the end to be able to open it as a clean out) and now it works perfectly, totally unaffected by whatever the wind does. (be sure to put some weep holes in the bottom of the horizontal 6" pipe to drain the condensation. The big test will be to see what happens to the condensate when it gets to 20 below. I may have to use expensive insulated pipe, or try wrapping it with fiber glass insulation and ten wrapping it some more with shrink wrap. Hopefully it will not come to that.

The 8" model from lomanco comes without the base, which you do not need. Becuase they make so few of them, you have to pay a lot more for the 8" vent than the 12" model, but I do not know if you can take the base off odf the 12 in model, and I think it might put up rtoo much wind resistance in a storm.

I had expected that the heat from the exhaust was going to make the vern turbine rotate in the absence of wind, as it would on a rook exhausting hot air in the attic. As it turns out, there is so little exhaust from the vent, that it will not make the turbine rotate when there is no wind, you just get water vapor consinging once it tits the cold air flowing thought the blades of the vent without turning it.

I just got my fire brick heat riser stove going a couple of days ago. But for example, this morning it's been running for 4 hours at about 500 degrees f at the lid (with some tweaks I am sure I can get it to go higher, it's been running fine, but i am using the full 4.5 width of the brick as the thickness of the riser, as opposed to some people who stack them on edge. Still, the insulation needs only allow the fire to remain hot while rising. I would think that even the 1.25 thin fire bricks on side would contain enough heat to keep the fire hot enough while rising. I would think that in no circumstance, with fire brick as a heat riser can you get enough heat bleed through to not allow the sides of the barrel to cool down that which comes out of the riser sufficiently so that it will contract in volume. This is a video of my prototype which I used, essentially unchanged in my current stove. It's 13 bricks high and I put a barrel over top, cutting a rectangular hole to allow the barrel to slip onover top of the heat riser and fire tunnel (that's what I call it anyway). In the video you will see that the half sawn bricks when laid up into an octagon form a star pattern. It is really quite pleasing to look at, with the star pattern reversing each course. But I am not so sure that the tips of the stars sticking out like that aren't flowing the down draft between the rise and barrel walls. It is relatively such a slight flow, I wouldn't think so, but if i had it to do over (and the time) when I cut the bricks in half, I would have also set up a jig to cut those tips off. Also, I would like to see the stove just a bit bore rockety, so when i get a chance, if we happen to get a warm spell, I will add another 12 inches to the barrel height which will allow me to stack the riser another 5 courses higher.

https://onedrive.live.com/?cid=373bc244e577ab46&id=373BC244E577AB46%21655&action=Share&v=3


The tick to sawing the bricks in half is EXACTITUDE. I used a table saw with a 10 inch diamond blade from home depot (about 20 bucks) do not buy the really expensive ones) Set up a "sled" that you can build a jig on to hold the brick exactly in place. make the jig so that you can make minute adjustments as to angle and the exact spot where the cut begins. Try it out by first using a wood blade on the say, cutting 4.5 x 9 pieces of OSB (flake board) and then switch over to to the diamond blade using bricks. You are going to waste several of them getting the cut just right. (save the pieces though) when propoerly cut, you should be able to put either half of one brick with either half of another, and it will form an EXACTLY straight brick. Also ytou should be able to take a half of one brick and put it on top of the other half of the smae brick and they will be EXACTLY alike. Also, you shoud be able to form the halves oif the same brick into a perfect 90 degree angle using a metal square with no gap at all between the square and the brick when measuring either the insider or outside corners. It seems like a lot of extra work, but you will thank yourself when stacking up the bricks, if you use the octagon design, that all of the brick surfaces come together with just a slight amount of adjustment. (I forgot to mention, make absolutely sure that your table saw blade is set EXACTLY perpendicular to the table saw surface)