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Post by szczepanek on Oct 17, 2019 3:45:51 GMT -8
Dear builders,
I've started the heating season with my new batch box. It works awesome, only there is more smoke from the chimney than it was with the J-tube I had before. Or it's just more smoke AT ONCE, as the total burning time is much shorter. Anyway, I want to minimise the smoke with what I've got now, hence this question.
The riser diameter is 20.6 cm.
According to Peter's table the primary air inlet should be 67 cm2. It's provided through that middle door, which is roughly 20x8 cm. In order to get the right size, I put the bits of firebrick on the left hand side of that door, so the hole I've got now is about 8x8 cm.
As I did the video, it was the second batch I put in, almost an hour into the burn. As the fire gets bigger, you can see and hear it making "waves" with the sound of a "hoo hoo hoo".
When I remove the bricks and let the air in through the entire door (160 cm2) this effect stops and the fire burns rapidly and steadily.
When I compromise the two modes and I put the bricks in a different way, so that the inlet is about 110 cm2, this effect is much softer and lasts shorter before the fire comes to a perfectly steady burn. Also, I have an impression that there is somewhat less smoke from the chimney in this case.
The firebox dimensions are all as they should be according to Peter's table EXCEPT I made it deeper - it's 75 cm rather than 60 cm. I don't know if it matters, but I'm telling you in case it does.
What do you think? What would be the optimal size of the inlet here? Thank you!
Jacek
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Post by satamax on Oct 17, 2019 5:00:12 GMT -8
Hi Jacek.
How did you find the metal first skin trick?
Well, your stove is pulsing, and i think with a longer firebox, the air inlet should be somewhat enlarged. Because you're burning more wood at once, you need more air.
About the smoke, are you sure it's smoke? Often it's condensation.
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Post by peterberg on Oct 17, 2019 6:51:43 GMT -8
I'd second Satamax here. It might be that the heater isn't dry yet and the chimney a bit too cold. In that case you need more air inlet opening. Air provision is a combination of inlet opening and air speed, low speed means larger opening and vice versa. So tuning your combination is in order, a slow pulse is not a good sign.
The heater is running in now, most if not all of what you see coming out of the chimney should be water vapor. When it's white and dissolves in the air within 2 meters it is definitely mostly water. When you have the chance, climb up the roof and have a sniff at the plume. When it smells vaguely like wet charcoal or wet socks (9-methyl ketone) it's very close to complete combustion.
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Post by gadget on Oct 22, 2019 19:13:33 GMT -8
I like that beveled door! Great looking heater.
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Post by esbjornaneer on Nov 4, 2019 10:25:19 GMT -8
How did you find the metal first skin trick? Max, did you not use a metal bell for one of your bells? Is it hijacking the thread to ask how yours behaved?
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Post by satamax on Nov 4, 2019 12:29:30 GMT -8
How did you find the metal first skin trick? Max, did you not use a metal bell for one of your bells? Is it hijacking the thread to ask how yours behaved? Works wonders! permies.com/t/44806/Cobbling-workshop-heater-cooktop-ovenExcept for the few design mistakes! The first metal bell, being part of the ceiling of the firebox. That killed the bottom there. But that was to be expected. There's pics in the permies thread. Fixed that for the moment with a refractory slab offcut above, and ashes. And i really regret having to "bend" the riser. If ever i re build another one, the window in the first bell, will be offset to the side, to build an oven. Originally, it was just meant to be able to assemble the dry stack riser, and check my fire. Also for cleaning.
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Post by szczepanek on Nov 19, 2019 5:22:32 GMT -8
Thank you guys! satamax I (re)invented the metal first skin trick myself. If you can call it so at all - in my case the metal box sits on top of the brick walls - there isn't any double skin in this heater. I'm happy to have learned about your cooktop over the firebox, thanks esbjornaneer for mentioning it. I'm just thinking about doing a thing like this for a friend. Maybe I should make a normal brick ceiling for the batch box firebox and cover it with a not-so-thick metal plate? I got this idea because the firebrick top of the firebox in my heater gets really hot and stays warm for over 10 hours after the burning. peterberg Thank you for the wet socks metaphor. Let me follow it and tell you that the smoke colour resembles that of white socks after three days of wearing. It's not black, not white to me, it's brownish. And that's after some 20 or 30 burns, so shouldn't the water be long gone by now? As you may expect, one batch burns within some 45 minutes, and I'd say the first half of that time is smokey and the latter half is clean. I's love to smell the smoke, but I don't want to climb onto the roof, unfortunately. The last time I did that I found myself in a position so awkward, that, if I were a cat, I would definitely start meowing in a way that makes people call the fire department. Only I wasn't a cat and there were no other beings around. I followed your advice in a way that I keep the primary air inlet twice as big as in the tables. And if it starts to pulse I remove the little bricks and I keep this little door fully open for some time.
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Post by satamax on Nov 20, 2019 13:55:06 GMT -8
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