Pea gravel versus sand

[matthewwalker]

Oct 15, 2013 8:35:24 GMT -8 Rick Thornton said:

But already the gracious and generous nature of this forum has armed me with better ideas which have seen me decide to locate the burn chamber and bench together down in the basement. My questions are thus:

With a concrete floor, is it advised to lay the half barrels directly on the floor and cob them in?

I would probably still lay down a layer of cob underneath the whole assembly Rick. It's not necessary, but for one, it will ensure a better seal, encapsulating the whole thing. Counter-intuitively, it will also be much easier to clean up if you decide it isn't a great location or want to make changes. I learned this the hard way. There's some big black rectangles on some local concrete around here! With cob, you just shovel it up in a wheelbarrow, and it's ready to build with again.

Oct 15, 2013 8:35:24 GMT -8 Rick Thornton said:

If I'm seeking to make the half barrels perform as bells, what would the holes in the ends of the barrels look like in terms of shape, size and location?

This one depends on how many bells, layout, etc. I usually just join them to create one big bell, so i cut out most of the "bottom" of the barrels, leaving a strap across the diameter to keep them from spreading. Someone here, Pinhead maybe, suggested joining the halves in a way where each was an individual bell. In this case, ports roughly equivalent to system CSA low to the ground, with inlet slightly higher than exit. I believe this is better for a short run, but potentially can stall if you try to go too big in terms of total volume of all bells.

Oct 15, 2013 8:35:24 GMT -8 Rick Thornton said:

How would I connect the half barrels? Butt them and just cob over?

Yes. You can even start slapping mud on all the gaps to seal and get burning pretty much immediately to test out different layouts and bell sizes/configurations.

Oct 15, 2013 8:35:24 GMT -8 Rick Thornton said:

As per Matt's idea, I'm building an 8" riser. How many half barrels would I want to link together?

See above. Or, conversely, how many do you want to link together. I've done as many as 11 halves, which I felt was a bit long but it worked, and as few as three. I think Pinhead did two halves as bells and reported he was really pulling the heat out of the system even with such a short run. Personally, I like mass for longer heating cycles, so I'm a fan of bigger mass runs.

Oct 15, 2013 8:35:24 GMT -8 Rick Thornton said:

There is an existing wood stove in the basement and I'm tempted to exhaust the RMH into the 6" metal flue that serves the stove. Are velocities and volumes going to permit exhausting into the existing 6" pipe that has about 20' of vertical distance before it exits the roof?

I think it will work, but you might have a finicky system and it may be hard to pin down where exactly the problem is if you throw too many variables at it. I'd be tempted to try it out though, and mess with the layout until that exhaust worked for you. It will be all about tuning to get the exhaust temps/speed just right, which will be a function of a lot of variables, including fuel, bell size, cobbed or not, wet/dry, and so on. Expect it to change as those variables change.

Good luck Rick, keep us posted please.