6" BBR plunge door and cob bracing

For a while now I've been pondering a BBR for my home.
I want to build a 6" BBR with a bell, possibly as a bench.

I really like some of the features of the 7 inch batch box rocket mass heater in the woodshop at wheaton labs such as:

gravity plunge door

no metal bracing used, but cob holds the core together

I'm wondering whether the plunge door could be implemented on a "Shorty core" if the necessary air channels are built into the frame it leans against.
I like that the Shorty doesn't rely on the secondary air channel that needs replacement.

Could the "cob" bracing work on a shorty core? Or are we entering weird experimental ground here?


Thanks in advance fellow RMH enthusiasts

I'm going to give my 2 cents on this and hopefully it will revive this post and we will get some more comments.

The plunge style door should work for this as long as the air intake specifications stay the same.

As for framing, I've never done any sort of metal bracing on my stoves and just use refractory cement for the core build and wrapped in cob.

Thank you Daniel for your insight.

Sure, the necessary air channels would be built into the frame of the door. And the whole door and frame unit would be leaning against the core. I hope it will be airtight enough. I’ll see what I can come up with.

Good news that you’ve built BBRs with just cob as framing. Do you have experience with the shorty too?

And a new question: did anyone try refractory shelves (kiln shelves) for the roof of the burn chamber of the shorty? Most I’ve seen are self cast refractory.

Thanks in advance

Peter's original Shorty experiments used pieces of kiln shelf for the top of the firebox and expansion chamber/riser.

Indeed, Peter uses kiln shelving for testing his experimental builds.
He has not recommended their use on permanent builds.
A peaked roof design with standard firebricks has been used on first-gen batch boxes; it could also be used on a Shorty core.

Thanks for the input.
I really wanted to use the inclined fire bricks but thought it wouldn’t work on shorty because they would be in the way of the exiting exhaust out of the riser, wouldn’t they?
Do you remember the reason for not using the shelves in a permanent build?

Apparently, the shelves aren't reliable in the long run.
For short-term use or on a build with easy access to the core, they would be fine.
Perhaps in your warmer climate, they might last indefinitely?

I originally thought first-gen batchboxes required a flat roof, but Peter oked the peaked design.
I suspect that it would work on Shorty as well.

thomas rubino wrote:Apparently, the shelves aren't reliable in the long run.
For short-term use or on a build with easy access to the core, they would be fine.
Perhaps in your warmer climate, they might last indefinitely?

I originally thought first-gen batchboxes required a flat roof, but Peter oked the peaked design.
I suspect that it would work on Shorty as well.

I have always built a peaked roof for the burn chamber-  the trick is simply in that you don't let bottom base side slide any where (out) .  NO different than a buttress, if the bottom can't slide it can't fall in.  If y our using a tension frame, just utilize a part of the frame on each side of the base of the peaked roof. thus one angle cut on one end of the brick and one angled cut on the base side.

If you need photos, let me know and I will look them up. I think this is/was shown in my build a few years ago, but attached to my postings.

if you don't have a brick saw, then I would suggest casting instead.  

Scott

Benjamin Dinkel wrote:Thanks for the input.
I really wanted to use the inclined fire bricks but thought it wouldn’t work on shorty because they would be in the way of the exiting exhaust out of the riser, wouldn’t they?
Do you remember the reason for not using the shelves in a permanent build?

The brick at 2.5" thick would be below the exiting exhaust. The smaller the size of the stove the shorter the two top brick would be, still cut for the taper as the other stove photos shown in this forum subject.