So it was a great weekend using my RMH. A lot was going on: we were stacking more thermal cob (never seems to end) and doing a burn to help dry it out.
But, the burn was only so-so. As a matter of fact when it was first lit there was a terrible smell, kinda like a chemical smell. If you've ever used the fire starters it was sort of like that, but, different.
And I'm willing to bet that if I could have seen the stack outside (it was night time) it would have been pouring black smoke out of it.
Then, the burn tunnel starts to "gulp" air. As though it could only take so much oxygen every two seconds or so. Finally after it got nice and hot everything seemed to settle down and draft fine, but, I still needed to cover the feed tube with a brick to help choke the system.
We were going to add more cob, but, I was troubled by something I had seen. I had noticed that the 55 gal. barrel top is concave, not convex, meaning that it looked like the top of the barrel was closer to the top of the heat riser than I had planned. Also, Matt, remember when I did my refractory pour that I said the inside bottom of the heat riser had pushed in a bit. Well, before we tucked this baby all the way in I decided to take apart the barrel and look at the insides.
So we broke the seal (cob) holding the barrel and lifted it off. I'm glad we did. Not because we saw anything glaring, but, because it's nice to see what things look like after half a dozen burns.
The barrel really bothered me and so I got a 2x4 and forced the center back to a convex (rounded) profile. Next I removed the 8" galv. pipe that was the interior of the heat riser. Looking at it after only six burns or so inside the heat riser made me cringe. Even if the buckling at the bottom didn't affect the burn it just frustrated me to leave it like it was. Flawed.
So, my wife told me to remove it and I did.
Much better.
So we cobbed everything back into place, level the 55 gal barrel and fired it up. No lie…best burn since I built it. Never needed to choke it down by covering the feed tube, no smoke back, no fire creep, smooth rocket sound. Nice.
So I just wanted to post this to say that little things can make a huge difference. The clearance between the heat riser and barrel makes a TREMENDOUS difference. The feed tube had been wide open for three burns now and the stack still stays at 150˚ or less.
So a recap for any new folks:
I thought the distance between the heat riser and the barrel was supposed to be 2-3 inches (after reading some other forum posts I've come to believe it can be a little bit more).
I thought MY distance was 2", but, if the barrel bottom (now the barrel top) isn't flat, or worst in my case convex, the you need to adjust for that. It's necessary for the push/pull of the system to work correctly.
Does this make sense? It seems to make to me because I saw the issue, but, I'm not sure it comes across in writing.
Ray