rocket mass heater question?

Has anyone tried a thicker walled bell or barrel in their design? Would a 1/4 " or more walled bell have the same required effects? As I presume  that the bells purpose is partly to create temperature variance for further draw. Any input would be much appreciated.

Hi, I have recently got my 6" batch style operational......When I built it I  had on hand an old 50 gallon  metal barrel from the 1920's, it is exceptionally heavy, 84 lbs to be exact.  twice as heavy as today's barrels and twice as thick. The only thing I have noticed its a few minutes slower in radiating heat.   my old wood stove which I replaced had 14 gauge metal as have today's barrels, they are lighter and faster to radiate to heat......as for draw I assume it has minimal effect as is absorbs  heat, the air volume diminishes and is routed downward through your mass in the same fashion a thinner bell would do. A tall stack adds to the exhaust draw also.
how high is your stack above the riser floor ?


Dave

Thanks for your input. I will build the stack to the required height as I have from the rocket mass heater.book by Erica and Ernie Wisner. Was just wondering if 2 foot gas pipe with sealed lid would be too thick a material 5/8"?

Steel is so conductive that, after a short delay in warming up the bell, I think it would work pretty much like a standard barrel. The major difference would be that it would hold and radiate heat for considerably longer than a standard barrel (but still nowhere near as long as a masonry bell).

Masonry bell is certainly worth considering. Thank you. For summer nights I often use a wood stove for heating water, drying produce etc. In replacing the wood stove with a rocket mass heater I was planning on closing off vents to the thermal mass , to exhaust straight from the  bells manifold duct. Allowing less heat to be stored  in the cabin. In warmer seasons ,  while keeping warming features.

This idea of a masonry bell is new to  me, but it would seem that it would store heat  even from short fires  just like the bench

Over a longer burn, it would seem to start to lessen the ability to radiate heat away quickly to keep the thermal differential inside the heater that pushes the exhaust gases out.

What am I missing here?

If you are depending on the push from the barrel for your draft, you might not want a masonry bell. If you have decent natural draft, there is no downside. Having a metal access panel in the bell for maintenance/inspection can give some of the instant heat benefit of a barrel.

thanks for verifying that, what about the idea of keeping heat out of the bench (and building) by using a masonry bell?  

bob day wrote:thanks for verifying that, what about the idea of keeping heat out of the bench (and building) by using a masonry bell?  

Can be done, no problem here. The top gap, being the space between riser top and barrel can be easily 20 times the recommended minimum. See my first iterations in rocket land, http://donkey32.proboards.com/thread/40
But you'll need a chimney stack, whatever you do. And I'm unable to tell you what the size of the bell should be combined with a given system size of a J-tube rocket.
Regarding batchrocket technology: more hard numbers are available including a spreadsheet to size a bell proportional to the system size. See batchrocket.eu/en

My 7 1/2" J-tube in a masonry bell has about 50-55 square feet of internal surface, 2 1/2" old brick bottom half and firebrick top half, plus 6" of cob shell. The exhaust through a temporary 6" stovepipe is almost touchable until a few hours of hard burning, and never gets over about 200F on the exterior surface near the bell, probably less. I have good natural draft, with only about 12' rise from firebox inlet to chimney top (will be extended another 5' before winter).

Glenn, I need to remember this, it looks like an 8" J-tube is on a par with a 6" batch box, output-wise. So that means both do need the same size of bell internal surface area. Interesting!