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New member: Why barrels and not bricks for the riser?  RSS feed

 
Posts: 17
Location: Delevan,NY
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I'm considering building one of these for a new wood shop.A conventional woodstove took the last shop in December.The temp of the riser spooks me though.Can it be built from bricks instead of a steel barrel?Do you have to have onlt 2" clearane beteeen the top of the innner riser and the top of the outer riser or can you go more?I can't imagine sawdust settling on a 500* top plate on the riser.Am i missing something here?my shop is 40x20 with about 18' to the peak,timberframe.
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A simple answer. Steel drums are inexpensive, available in many countries and requires minimal time and skill to setup. The steel drum is also efficient for immediate radiant heat transfer. Whereas brick acts as thermal mass to store and slowly dissipate heat over a period of time.

The 2" gap is part of what creates the draw. The other parts are the length of the height of the feed channel, the burn chamber and the height of the exhaust channel. In a nutshell; the shorter the exhaust channel, the greater the gap. However, you do want a lengthy exhaust channel as that is where the draft begins. The basic furnace\fireplace operates on a pull system, not a push system.
 
Paul Ebert
Posts: 17
Location: Delevan,NY
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Thanks for your reponses.
 
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Hi Paul,

As both a traditional Timberwright and "teacher of all things fire related" I understand your concern for not having another shop go up in smoke. In your case, if you can get brick, use them, or use a barrel for the benefits described and reduce the horizontal "flash area" of the top by placing a large thick layer of clay, or better, soapstone. In general a rocket stove is going to be much less of a risk than any other "homemade" wood burning device.

Regards,

j
 
Paul Ebert
Posts: 17
Location: Delevan,NY
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Thanks Jay,good idea with the stone.I have access to alot of large slate flag stone .what do you think of basically building a stone barrel around the drum with maybe a couple of inches of air space between to avoid a very hot spot? how long would this drum last in one of these mass burners?Maybe i should build two brick barrels with the same air space between?
i was sent a link to the "Dragon Heaters" site.i like the looks of their Castle built model.Any opinion on them?
 
Jay C. White Cloud
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Hi Paul,

I have only dabbled with "dragon stoves" liking more traditional building modalities of kang, ondol and other masonry heating, or wood burning systems, which the dragons all share a heritage with. What I do like about dragons in general, is the ease of assembly and severability. When you start make the modification you describe you negate that benefit. Simply placing a large flat rock on the horizontal surface will achieve 90% or more of your desired effect, without going backwards in design benefits of the dragon. If you stay on top of routine maintenance, keep the shop neat and orderly, and apply a good fire retardant to all installed wood or combustible surfaces you will negate much of the burn hazards in the shop...plus keep all combustible fluids, rages and the related finishing products in a metal fire retention locker.

Regards,

j.
 
Paul Ebert
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Location: Delevan,NY
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Thanks Jay ,again. If you have any links to those other style stoves,please pass them along.I'd love to see how they are made.too.I'll do some searching.
 
Jay C. White Cloud
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Google searches will give all I can, short of what's in my noggin, books or files.

The fire suppressant can be had by contacting my friend Steve Sass, and asking to pick his brain about this. He will give you all you need to know.
 
Mother Tree
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Paul Ebert wrote:
i was sent a link to the "Dragon Heaters" site.i like the looks of their Castle built model.Any opinion on them?



I sincerely hope you're not telling us that a member is using the PM system to advertise their own site as that would be a gross abuse of membership. Possibly a banning offense. I trust it won't happen again.
 
Paul Ebert
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Location: Delevan,NY
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Burra Maluca wrote:

Paul Ebert wrote:
i was sent a link to the "Dragon Heaters" site.i like the looks of their Castle built model.Any opinion on them?



I sincerely hope you're not telling us that a member is using the PM system to advertise their own site as that would be a gross abuse of membership. Possibly a banning offense. I trust it won't happen again.



No ,I mentioned it on another site and got a reponse about them.But seriously,it was exactly what i was talking about in concept.You guys have some strict rules around here.i guess I better not mention my furniture business to anyone.hah
 
Posts: 243
Location: near Houston, TX; zone 8b
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If you are building a rocket heater on a wood floor, you need to incorporate an air gap between the wood and your burn tunnel. The layers might be the wood floor, stone, bricks to create air gap, another piece of stone, then, the burn tunnel. A detailed recommendation for this is found in the 3rd edition of rocket mass heaters on page 68.

The burn tunnels do get very hot and because the fire is usually down lower than in a cast iron stove, the wood floor is subject to spontaneous combustion without proper precautions.
 
Paul Ebert
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Location: Delevan,NY
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Cindy Mathieu wrote:If you are building a rocket heater on a wood floor, you need to incorporate an air gap between the wood and your burn tunnel. The layers might be the wood floor, stone, bricks to create air gap, another piece of stone, then, the burn tunnel. A detailed recommendation for this is found in the 3rd edition of Rocket Mass Heaters on page 68.

The burn tunnels do get very hot and because the fire is usually down lower than in a cast iron stove, the wood floor is subject to spontaneous combustion without proper precautions.



Thanks Cindy.your units look great.This lower /underneath the burner spot seems like a good place to install small fan or two to draw air and heat out to add to the heater's efficiency. The fans could easily be run by a small solar panel or minimal electricity.This would keep the floor cooler also.
 
Jay C. White Cloud
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Paul, I will say this about "convective currents" (fans)...watch there use.

About the only place I will put a fan is in the flue assembly itself someplace (usually by the exhaust end) and that is usually a heat resistant "squirrel cage" to assist with initial draw if the flue is not up for it due to height or distance from burn chamber and/or too many twist and turns not equalling the "natural" draw effect of the rise in the discharge flue.

Fans to move warm air around often (very often) do more to "cool" the air than actually distribute it. If you place a person in 85 degree F water or blow air of this temperature on them...they will become hypothermic in a short time. The air (or water) seems warm but it is not our body temperature and when you and the "convection effect" it actually cools. Let heat move naturally and rely more on proper design of space to let these "thermal stratums" form and move about. This is why "radiant" heat is so superior to "convective" heat warmth.

Regards,

j
 
Paul Ebert
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Location: Delevan,NY
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Jay,That makes sense.I would still use one in my application to assure the floor doesn't get too hot.FWIW.
My shop will 20x40 and have an 18' high peak, open to it from the floor. What size setup would be recomemmended for this area?8",6" two 4"?
 
Jay C. White Cloud
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Hi Paul,

Assuming you are asking about "flue fans," in the past I have really had to "experiment" as I like to use the bare minimum, but you don't get a lot to choose from. Also, it is more about CFM they can move than inch size.

Regards,

j
 
Cindy Mathieu
Posts: 243
Location: near Houston, TX; zone 8b
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I would still use one in my application to assure the floor doesn't get too hot.



If you leave a few inches of space under the burn tunnel, you don't need to use a fan under the burn tunnel. The floor will stay cool enough without the fan. You could also install a thermocouple at the top of the floor to make sure it wasn't getting too hot.
 
Paul Ebert
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Location: Delevan,NY
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I was asking about burner size to heat a shop this size.
 
Jay C. White Cloud
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I would probably go larger than smaller as a bigger unit can be run less and a smaller unit may not produce enough if the shop doors are opened often, but this view is subjective on my part.
 
Paul Ebert
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Location: Delevan,NY
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what about two smaller 4" models side by side.The second as a back up in really cold times.The smaller first to avoid too much heat yet allow for mass when it goes out?Could you run both burners into the same group of flues and mass pipes?Maybe I'm overthinking this,hah.
 
Jay C. White Cloud
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Maybe I'm overthinking this,hah.



I believe this may be the case...
 
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