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Rocket Heater Masonry Stove Built using Flue pipes and a Dragon Burner  RSS feed

 
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We were looking for a simple way to build a bell style masonry heater. This build does not use a barrel that is commonly used in rocket heater designs. However it does use the standard J-tube combustion chamber with feed tube, burn tunnel and heat riser. We decided to try using commonly available chimney flue pipe sizes to construct a quick and dirty masonry heater using a dragon burner as the combustion chamber.

The 1st revision had some issues and we just completed the build and testing of the 2nd rev. We have a few small changes we will make to the design, but in general we were very pleased with it. Although the heat riser exit temperature tipped 1500F, the chimney exit temperature never exceeded 180F. The stove radiated a lot of heat for many hours after the burn. It was still warm over 6 hours after the fire.

This design has:

Very small total footprint (30"x36')
Drafts well even in summer
Low CO emissions (typically less than 300 ppm)
High efficiency (85-92%)
Captures all of the heat (chimney exit temps 120-155F)
Can be constructed in a day
Is inexpensive and simple to build

The 2 pictures show the actual build and a sketchup of a possible tile and stone skin covering for the stove.

Notes on the build are here.

http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-3/

And the data charts for the build here.

http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-3/
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Location: SW Missouri
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This may be a dumb question, but how does the air flow through the towers?
Can you do a drawing for the less perceptive people?

Thanks,
MartinE
 
pollinator
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Location: La Palma (Canary island) Zone 11
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Well, just go to the blog, Sandy sells those products like the dragon burner.
 
Sandy Mathieu
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This design is based on using bells rather than flues. You can read more about bells here.

http://blog.dragonheaters.com/wood-heat-storage-flues-vs-bells/

The blue tower is the heat riser, there is an opening from this heat riser tower to the larger of the 2 columns. The larger column is the 1st bell. The warmer gases rise while the cooler ones sink. There is an opening at the very bottom between the 2 large towers. The cooler gases move from the 1st bell (tower) to the second (shorter tower), where the same thing happens, hotter gases rise, and cooler ones are on the floor and are exhausted out the chimney pipe.

This approach traps hot gases in the towers until they have lost enough heat to sink and be exhausted. It does not have a traditional gas path, where all the exhaust moves through a prescribed channel or path.

In the 1st 2 pictures from the blog build notes you can see the opening between the heat riser tower and the 1st bell. The 3rd picture shows how bottom of the 2 bells. As you can see the 2 bells are open at the bottom.

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Sandy Mathieu
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I can not figure out how to edit the above post, but the link to part 2 wit the build notes is here.

http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-2/

I have also added an update to the build and its results here.

http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-5/

It went well, we are very happy with the results, and now feel it is solid design. So next up we will be covering in stone and other materials for a finished look!
 
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Location: Colorado Rockies, off grid
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Thank you so much, Sandy, for sharing your experience. I love the look of this system so much more than 55 gallon barrels! Can you help me by answering a few questions? I hope to begin building as soon as I've put together more money to buy the parts.

In the RMH 55 gallon barrel design, the smoke from the heat riser goes up 1.5 - 2 inches, hits the top of the barrel, then flows all the way to the bottom of the barrel before exiting into the mass storage or bell. In your design, as near as I can understand by studying the pictures, there is an opening into the first bell that is at the same height as the top of the heat riser, and there is no flow to the base of the heat riser because it is completely insulated around the heat riser inside of the ceramic flue. Have I understood this correctly?

1. Is there any difference in the draw between the design that calls for the smoke to be pulled down to the base of the 55 gallon drum before exiting into a mass storage or bell, and the design that has the heat riser completely insulated with no space on the sides, and the smoke being drawn directly into the bell from that height? What does this do to the draw inside that first bell to have the entrance into the bell more than a third higher than the base?

2. Why is the top of the ceramic flue in the heat riser column so much higher than the top of the heat riser? With the opening into the first bell right at the same height, would the draw pull the smoke into the bell, or would the smoke first rise to the top of that column, and then gradually be forced out because it is effectively a bell above the heat riser, and once filled with hot gasses, would then flow into the first bell?

3. Would it be possible to have the opening into the first bell smaller (like about 2 inches), and the top of that column end right there at the opening, so that the heat would hit the top of that column and provide a cooking surface as it is exiting into the first bell? Would it exit into the bell with only a 2 inch high hole, or would it not draw properly and back up into the room?

4. Could the surface of that first column be made out of sheet metal welded to the top of the column with fire clay so that it would become very hot as a cooking surface?

5. I don't have any desire to be able to put tiles on the outside of the columns. Do I really need the fire bricks inside the column, or could I simply fill the space with insulation (what I have is perlite), and then cover with fire clay? That would be far less expensive and the lack of money is a serious consideration (I am 65 and live very simply in wilderness on a low retirement income).

6. Why is the first bell a foot taller than the second bell? Does this help the draw?

7. Why is the ash pit hole above the ground surface? Would it be possible to make that ash pit hole level with the base of the towers so that it would be easier to scrape out the ashes? I really like the design of cleaning out ashes with your system - it appears to be possible to clean out the entire base of all of it. With the barrel design, there are areas that simply cannot be reached for ash cleanout.

I hope you can help with these questions, because I'd like to start building as soon as possible.
Thank you,
Lua
 
Sandy Mathieu
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In the RMH 55 gallon barrel design, the smoke from the heat riser goes up 1.5 - 2 inches, hits the top of the barrel, then flows all the way to the bottom of the barrel before exiting into the mass storage or bell. In your design, as near as I can understand by studying the pictures, there is an opening into the first bell that is at the same height as the top of the heat riser, and there is no flow to the base of the heat riser because it is completely insulated around the heat riser inside of the ceramic flue. Have I understood this correctly?



Yes

1. Is there any difference in the draw between the design that calls for the smoke to be pulled down to the base of the 55 gallon drum before exiting into a mass storage or bell, and the design that has the heat riser completely insulated with no space on the sides, and the smoke being drawn directly into the bell from that height? What does this do to the draw inside that first bell to have the entrance into the bell more than a third higher than the base?



No one can say what the draw of a cob bench type design is because it hasn’t been tested (as far as we know). A particular piece of testing equipment is required in order to determine the draw. However, having said that, bell designs typically draw better than flues, because they are more efficient at heat capture. Traditional rocket heaters are flue systems and this is a bell system. Bell systems create intentional pockets for hot exhaust to collect in and cooler air to escapes via a much shorter route. You can read more about flues vs bells on the blog. The draw of this system is excellent; it worked just fine even when the outside temperature was over 94°F.

Why is the top of the ceramic flue in the heat riser column so much higher than the top of the heat riser? With the opening into the first bell right at the same height, would the draw pull the smoke into the bell, or would the smoke first rise to the top of that column, and then gradually be forced out because it is effectively a bell above the heat riser, and once filled with hot gasses, would then flow into the first bell?



We wanted a large opening between the heat riser and the first bell, to achieve good draft. Also experiments have shown that the best results are achieved with about a foot above the heat riser. The area above the heat riser is probably too small to really constitute a bell where gases have time to sort themselves out.

3. Would it be possible to have the opening into the first bell smaller (like about 2 inches), and the top of that column end right there at the opening, so that the heat would hit the top of that column and provide a cooking surface as it is exiting into the first bell? Would it exit into the bell with only a 2 inch high hole, or would it not draw properly and back up into the room?



2" would not be enough cross sectional area. Did you see the cooking stove on the blog. It has a cast iron cook top. We were thinking of using a 4” core with its shorter heat riser. With the 6” core, the cast iron surface would be at an inconvenient height.

It needs 6" clearance for draft

5. I don't have any desire to be able to put tiles on the outside of the columns. Do I really need the fire bricks inside the column, or could I simply fill the space with insulation (what I have is perlite), and then cover with fire clay? That would be far less expensive and the lack of money is a serious consideration (I am 65 and live very simply in wilderness on a low retirement income).



Only about 12 firebricks are required. A gas seal is needed between the flue surrounding the heat riser and the inside flue liner of the 1st bell. You can also use cut off pieces of flue left over from the build, rather than fire brick.

6. Why is the first bell a foot taller than the second bell? Does this help the draw?

Most of the heat is taken out in the 1st bell, therefor it needs to be bigger.

7. Why is the ash pit hole above the ground surface? Would it be possible to make that ash pit hole level with the base of the towers so that it would be easier to scrape out the ashes? I really like the design of cleaning out ashes with your system - it appears to be possible to clean out the entire base of all of it. With the barrel design, there are areas that simply cannot be reached for ash cleanout.

We were designing for a cast iron clean-out door. It is not strictly necessary. As long as you have a gas-tight seal around the clean-out cut, you can make it as floor level. Making it gas tight is easily done with ceramic fiber paper or tape.


 
Lua Sage
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Thank you, again, Sandy, for the answers. Once businesses opened this morning, I called a local furnace supplier and asked for prices on the furnace flues. I figured a total of 13 one foot sections 17X17 for the two bell towers, 4 one foot sections 13X17 for the heat riser, and 7 one foot sections 15X15 for the liner of the first bell tower. I was quoted a price of close to $500, which is completely unaffordable for me. Am I looking at the wrong materials?
Lua
 
Posts: 243
Location: near Houston, TX; zone 8b
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Lua Sage wrote:Am I looking at the wrong materials?Lua



You are not looking at the wrong materials. I am sympathetic with your situation. We are trying to achieve (most of) the heat storage of a masonry heater at a fraction of the price. However, a fraction of the price may still be out of your budget.

If you are trying to heat a small place, you could go with a 4" model. We have not worked out all the sizes for the 4" yet, but the smaller flue liners are way less expensive than the larger ones. Check out our website (DragonHeaters dot com) and send us an email privately and we will see what can be worked out.

Cindy
 
Lua Sage
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Thank you, Cindy, I will do so. One question that might be helpful to others though, is "what does small mean?" My house is two rooms and a total of 700sf interior with very high insulation value (straw bale where the stove will be, stick frame with R19 and R30 insulation, plus reflectix foil on walls and ceiling in the other room.) What I'm trying to accomplish is reducing our firewood needs from 5 to 2 cords.
Lua
 
Sandy Mathieu
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So part 5 is out here is picture of the build with stacked stone.

http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-5-2/



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Lua Sage
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Beautiful. Simply beautiful. You are clearly artists.

I have decided to build and install the jet stove itself and forego a storage medium at this point. I simply cannot afford the materials and need to get an operational stove in place before October cold comes in. After talking with Cindy, I've learned a lot more about the whole process, including the need for an exit temperature of at least 140 degrees, so as to have no problem with condensation. Granted, I live in very low humidity Colorado and will be burning very dry wood, but it's still an important consideration, and I'm not at all sure that I know enough to design a bell or flue system that will work well enough. I have one chance - simply can't afford experiments that are possible do- overs. I do think I'll put up some bricks in a radiated circle around the barrel to catch more heat after it's built.
 
Posts: 106
Location: Sandpoint, Idaho
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Sandy, Very nice design! How many sq ft will this heat? thanks Al
 
Sandy Mathieu
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Probably in the 1500 sq ft range, but here is a link to the btus for each of the different sizes, it depends on how well insulated your home is, your climate etc.

https://store-lmpge.mybigcommerce.com/content/dragonheatercastleweblit.pdf
 
Alan Mikoleit
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Are there other ways to make these rocket heater bell stoves such as using large diameter metal pipes or tanks that get covered with cob and or rocks? Today I found some free steel pipe that is 18 inches in diameter and about 1/8 thick. thanks Al
 
Cindy Mathieu
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Steel loses integrity at 1,000°F; stainless will go a lot higher depending on its grade. If your rocket heater is working well, you will be getting temperatures in the burn tunnel of 1,500 or more.

So, many people have made stoves from steel and they work really well as long as the steel holds up, which isn't very long.

Steel pipe is good for many other things, though. You should hang onto it. You can use it as a pier to support a porch on a building, for example. It would be a waste to burn it up as a combustion chamber of a rocket heater.
 
Alan Mikoleit
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Cindy, I know to use fire brick for the burn tunnel and riser. You would not use 18 inch diameter pipe for those any way. I am asking about replacing the 17 inch square flues with 18 inch diameter steel pipe. thanks Alan
 
Sandy Mathieu
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Alan Mikoleit wrote:Cindy, I know to use fire brick for the burn tunnel and riser. You would not use 18 inch diameter pipe for those any way. I am asking about replacing the 17 inch square flues with 18 inch diameter steel pipe. thanks Alan



I think if you painted it with stove paint you could use them. Someone else would need to speak to how the cob could be attached to the steel. But theoretically it should work. You will need to protect the zone from the heat riser into the interior of your steel bell from the extreme high temperatures right in that zone. But once it hits the bell, the heat begins to dissipate a lot.
 
Alan Mikoleit
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This is a conception of a rocket bell heater I would like to build using 30 gallon barrels that are 18.5 inches in diameter. They will get covered with natural rock from this property. I used the 4 ft, 6ft, and 7ft heights from the flue bell heater design. This could be a very quick, simple, low cost heater. Alan
heater.jpg
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conception of bell heater using 30 gallon barrels
 
Alan Mikoleit
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Today a friend asked me why not use water tanks instead of barrels. So we drove to the dump and found a free water tank I was hoping the inside tank would be 16" diameter and it was! The inside area of the 17 inch square flues is just slightly more than the area of the 16" diameter tank. Hopefully water tanks are standardized so I can splice them together easy. I will just tack weld them and tape the seams. When I take the outside tank cover to the scrap yard I will get paid for this tank! I have a tile pad under my wood stove and I am going to raise it by 16 inches with cement blocks so the fire box input is up off the ground like on a masonry stove. My ceiling above the stove is about 15 feet so the high bell won't be a problem. I will document this build from as is to completion. And now to find a few more tanks, and buy fire bricks. Alan
 
pollinator
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Alan Mikoleit : Almost all hot water tanks fail for the same reasons, leaks, very few are replaced as part of a routine maintenance, There is a sacrificial Anion Rod that helps
to prevent corrosion and rust from forming, and the interior of the tanks have several coats of an ceramic glass coating, often the anion rod is not periodically replaced, some
times an electrical element fails and the person thinks that really tighten ing down the replacement part will guarantee no leaks, (some are held in place with a gasket and four
short bolts, and some use a threaded fitting and gasket ) Over tightening can cause micro cracks that will only get bigger. Some heaters fill up with mineral deposits and the
lower heating element fails because the mineral deposits act like insulation and the element turns the water into steam, with no water to keep it relatively cool ~ 140 dF ~ it
over heats and fails, cleaning up the resulting mess and flushing out the mineral deposits, results in hours of fiddling work, and it is often cheaper to replace an electric hot
water heater, than to pay a Plumber to do the job, some times the tanks threaded female fittings are damaged and some times a bolt breaks off preventing a good seal !

There are at least two more planed penetrations of the tank. One is the 3/4 iron pipe threaded opening for The pop-of valve, designed to open up and release water if it is too
hot, or there is a too high pressure condition like what happens when the lower electrical heating unit, buried in mineral deposits, produces steam and steam pressure just before
it fails (sometimes catastrophically)

The second planed penetration on the side of the tank down near its bottom, it too has a 3/4' iron pipe thread opening to receive a hose bib, that may be made totally out of
plastic, this is supposed to be there to let you periodically empty out the water in your tank and then allow you to flush out the Mineral deposits! This little task is supposed to
be done yearly in every home in america with out a water softener! ( that is most of them !) There are a few more planned penetrations with gas and oil fired hot water
heaters !

Water Heaters are often used with both ends cut out, to make culverts in ditches for light trucks and 4-wheelers to cross over on ! This can cause an area to be stripped bare
in very localized regions !

Take a close look at all penetrations, grinding while effective, will speed micro fractures in your ceramic lining ! I think if you are lucky you should have little trouble, finding 3
tanks that will last much longer than a 55 gal drum !

I will look forward to the dialog and pictures to follow ! For the Craft ! Big AL !

 
Alan Mikoleit
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Al 2 Al, thanks for all of your help and encouragement! A friend has another tank for me so I just need 2 more. The inside of the tank I got today is in perfect condition.
 
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Lua Sage wrote:Beautiful. Simply beautiful. You are clearly artists.

I have decided to build and install the jet stove itself and forego a storage medium at this point. ...



Lua, How'd the heater work out?
 
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Hi Sandy,

Thank you very much for posting these photos and data for us all to review.

My question:
Do I understand that the main reason you chose the large ceramic flue pipe is "quick, one-day installation"? I understand that ceramic has some thermal mass, but is mostly an insulator. I was wondering if you would consider building Bell-1 and Bell-2 completely out of cob (using a 14" form to get the same volume / shape). What are your thoughts?

Or

Is the point of the ceramic flue the 'smooth internal texture', which prevents a lot of build-up of ash, soot, or creosote? If this is the case, then would a cob wall be too rough, and act as a collector?


Another question:
If I have a super-insulated house (strawbale) and am living in New England, what house-size would you recommend for a 4" core vs. a 6" core? I don't want to over/under estimate the size of core I need.



Oh! And do you make the SketchUp models available anywhere? I'd love to drop exactly these models into my house plan.


Thank you!


-Scott
 
Cindy Mathieu
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A main advantage of the terracotta chimney flue liners is their structure. They are self-supporting.

We have a chart on our Dragon Heaters blog which addresses the thermal mass issue. Cob vs. terracotta not much difference from a conductivity and heat storage point of view. Terracotta flue liners have to be insulated from temperature changes greater than 50°F per hour. So, we recommend lining the first bell with standard fireclay brick splits (1.5" thick). The fireclay bricks do store heat better than cob or terracotta, so that makes the castle build more like a masonry heater. Fireclay brick material has the best price/performance for conductivity and heat storage.

Cob makes the working environment slick which can result in injuries or falls when walking around. We are not fans of cob.

We are using Peter van den Berg's design for the J-tube rocket heater; we have tested its efficiency and published the results. (You may be able to find the sketchup drawings of his J-tubes on line.) His design burns so efficiently there is no build-up of creosote or soot. Our designs recommend installation of a cleanout door for use once a year to get rid of ash at the bottom of the bells.

We have a chart with the relative BTU's per hour of the 3 sizes of burn tunnel which we sell. You need to know how many BTU's are needed for your house.

IMHO, the 4" needs to be tended way too often in order to keep the burn going. I would recommend a 6" because of this issue.
 
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