Bucket Forms --- as Heat Battery

[larsmith]

I'm thinking that Bucket Forms would come in handy, either using Cob or ReadMix, to act as a heat battery, for those who're burying their exhaust lines in a cob bench.

In my case, I'm burying my heat battery in sand ( the whole floor of my new addition / heater room is sand / clay ).

It wasn't till today that I figured that I could build some bucket-formed "pipes", lay them below-grade in my sand-floor, encase them in cobb and then cover them in the sand.

I'm not going to need much of a "heat battery", since my design incorporates more fire brick & red brick ( almost like a traditional masonry heater ) ... and if I'm careful, I can build a length of heat battery / bench, using the bucket formed channel, one length at a time, till I find the best length for my heat battery to absorb just enough of the heat from my heater while leaving enough heat to keep my draft going.

Comments ?

[canyon]

Sounds like a great idea! I guess I'd be concerned about the drag of the internal rough surface though(if cob). Maybe you could come up with a sturdy fireclay plaster to line it with(oversize your inner form appropriately). Also, you could incorporate into the form a bell end system like drain tile has so they could fit into each other to make more gas tight. Good luck and please share the results!

[larsmith]

I'd imagine that a "key" of some sort could be incorporated into the mold so that there was, perhaps, a "male" and a "female" end to the completed sections ... and that if done carefully, the 2 ends could fit comfortably together in a manner which would reduce out-gassing between sections.

Now to put on my design / materials hats and see if I can come up with a means of designing a form which will work. Not as simple as just adding the appropriate ends, since shrinkage of one section may be different and/or perhaps not as uniform as any other section, making it a challenge to join the 2 sections together. This'll make for an interesting "discovery" session !!

TY for another great idea.

Anyone else wanna jump in on this one ?

[Donkey]

Great idea..
The one(s) nearest the hot bits will probably crack. You could make just the first one of something more heat resistant. Vary the mix, ya know? Use grog instead of sand and no straw or something like that. After that they can be pretty well straight 'ol run-o-the-mill cob..
The ends don't really need to key together all that well. Since yer makin' the tubes of cob, just cob up the seams well..

I would recommend that you CAREFULLY check for CO leakage. I've said it a couple (few?) times on these boards already. It's my feeling that it should be fine, like brick. Exhaust gasses should follow the path of least resistance and go out the pipe(s). STILL, cob is porous and could leak and no one has yet tested the theory (that I know of).

[larsmith]

As some may know re: my design, I've opted to use FireBrick to form three separate exhaust channels down the left, the right and the back of my heat riser, adding to the thermal mass. From there, there will be a common "exhaust box" at the base of the heat riser, heading out to my exhaust. The weight of that much brick will be about a half ton, if my calculations are correct. Besides that inner portion, I plan to wrap the whole thang with redbrick, in a "masonry heater" style.

After I build the heater, I'm going to test the exit gas temp to see how much exhaust channel I'll have to build in order to absorb as much heat as practical before exhausting out of the building.

I've mentioned using cob but am open to using Quikrete or any other concoction which would act as a practical / safe heat battery.

[chronictom]

for the 'key part', just add make the one end 'vee' in and the other 'vee' out slightly. Add some cob around the bottom edge of the pail and line with a garbage bag first, that would give you the out vee, when you fill it, just leave it funnel shaped on top. cob between them. Although not needed, they will ensure that your channel is all lined up with no guess work.

[Donkey]

Well.. Your floor is mostly sand, yes??
Just burying the thing in the floor would count as "heat battery".
If I remember correctly, you have enough brick to do the job, why not build a brick channel through your floor? Bury it a few inches deep and cap it with something that is not likely to break when you walk on it. I know it's been mentioned before and it sounds like the simplest thing.

Though it would be quite a bit more work, chronictom's notion above would most likely work as well.. I don't think regular 'ol concrete will stand up the heat shock (assuming high temps around the entry to the channel). The arrangement you plan should soak up quite a bit of heat before it gets to the channel, so perhaps it ain't an issue. ??

[larsmith]

Construction of the heater has begun yesterday. First 2 Courses put in place by a professional brick mason ( tho his major is in cinderblock, not fire brick ). Each evening this weekend, I'll lay up some more of the brick till I've got the heat riser in place. Will report back ASAP with progress & test results.

I've purchased rabbit-cage "mesh" wire to create the initial form of my exhaust box, to which I'll connect my clean out and and exhaust. I'll cob it up well, trying to facilitate both the clean out and adequate exhaust.

Say a little prayer for this rookie.

[chronictom]

I was worried about using any type of metal mesh in it for two reasons...

1) will the metal and the cob expanding and contracting at different speeds cause problems?
2) will the metal melt, and if it did, would it really matter seems its already embedded?

[larsmith]

I plan to use the wire exclusively as an "arched" support, kind of the way old stone bridges and stone arches masons would build a wooden support. The mesh will not be embeded in the cob but simply the cob will rest on the mesh till it cures. As for what happens to the mesh after that point, I'm banking on it not creating any problems for me. If any have info or experience to the contrary, I'll thank you for any warnings you might offer. I'll not be taking this step for some time, as I'll be building the unit up over the next few days and am no where near building this "exhaust box" presently.

[chronictom]

in that case I can't see it being a problem... worst case scenario is it would melt and leave a thin layer or bumps on the bottom, but nothing that could cause issues...

[Donkey]

I see no problem with this basic idea.
A word of advice. Cob is quite heavy, though even a thin layer has a good deal of strength.
press a SMALL amount into the wire, cover the works just slightly. Let it dry completely and you will have a remarkably strong little arch to cob over.
If you just bury the wire in cob, it's a pretty sure bet that it will collapse on you.