6" to 8" Conversion at the seacow

[mannytheseacow]

Without derailing another thread, I thought I'd post about the draw on my system here instead.

I don't think it's related to my bench or chimney. My chimney is 7 1/2" square all the way up to my roof, where it transitions to 6" round. I had the same issues with my 6" system as well as other stoves I've build with mass attached (my cook stove is the first stove I've built that doesn't smoke, but I also haven't fired it indoors yet).

I'm pretty sure the flame creep and resulting smoke is a vector of the fuel I have. Very large surface area and very high density. I can pack my feed with 20 small sticks and it fires beautifully. I can fill that same space with 3 large splits and the tops will be burning before bottom cores are gone. Putting a pot over it solves that issue but long story short I'd love to stick large chunks in there and forget about it. Seems like deepening the feed and making a hinged door on top would solve that problem but I'm open to other suggestions.

[hpmer]

How does it run if you mix the two sizes? I find mine run best with a mix of sizes. I often use a big piece and several smaller ones which I think helps the draft and they all seem to feed off each other with more flame, which means more heat, which means better draft.

[ByronC]

It could be several little things adding up on you Manny.

First thing that came to mind, is there anyway to take the 6" (CSA=30 sq. in.) top section off the 7.5" x 7.5" (CSA=56 sq. in.) chimney for a quick test?

Yeah, that 6" batch box Matt put together is tempting me to go the same route on my indoor system build. One advantage of the batch box is less hands on tinkering with during a burn as opposed to a J-tube.

[matt walker]

I do wonder about that top bit being 6", but I agree that more likely it's your fuel. I have basically no experience with hard wood the likes of yours in my heaters, so I suppose comparing our experiences isn't fair. I did build that 6" J in NYC and we used oak, and it coaled up something fierce and was more prone to smoke back than any other heater I've built. I chalked it up to dense firebrick super heating the top of the fuel, which was for sure an issue, but fuel played a role as well. I do think it would be worth removing the 6" restriction temporarily if it's as simple as lifting it off the masonry chimney, just to rule it out. If that's not possible, well, even if it is an issue it's not a show stopper and your solution may work. It's worth experimenting with for sure.

[ByronC]

I've noticed the same with oak, or red oak in my case. It really needs about 3 years of drying time in a nicely roofed woodshed. 1 years worth of drying just didn't cut it, not for my knockoff quadrafire box stove. Even after 3 years drying I would have to split it down to 2" logs to get the stuff to burn hot.

[thickstrings]

Manny, one thing I tried in the 4"er I made was ...after there was a coal bed, I just stuck in 1 piece about 2 1/2-3" in diameter it worked pretty good til the coals diminished. By then the stick of wood was about 1/2 the length and I pushed it in.... It was Red oak.

[mannytheseacow]

Thanks for the input guys. Sorry to sound like I'm whining- I could have made that post a lot simpler to say big wood = smoke. I'm mostly burning red elm and walnut right now with the occasional hickory and oak. I have it split into irregularly shaped pieces sometimes over 6" across. What really got me thinking about the fuel was the testo results showing a burn around 30 minutes. Shoot, if I cram 3 of these big pieces in my stove after a full hour the won't have even dropped yet and it will be over 2 hours til they're reduced to coals. Add to this the stringy nature of these species of wood- the little strings tend to burn up the sides. It all seems pretty clear in my mind what's happening, just looking for the cure.

I can reduce the effect by using the bypass on this new stove so I tend to think it's not the chimney. It's easy enough to take that 6" stub off the end, though. It's just cobbed on to the masonry chimney. I'll pull it off next time I'm up there and see if there is a difference.

[mannytheseacow]

I added about 8" to my feed and so far so good. I can't explain the science behind it but I've put two loads through and no issues yet. I also left a small air gap in the front so that when there's a pot over it there's still a good air intake. Obviously it's still very wet and subject to change... No more balancing a pot on top of sticks at least.

[pa_friendly_guy]

That sounds like a good plan Manny. I have wondered why more people did not extend the fire box to hold longer sticks. I was wondering, as you extended it did you taper it wider as you went up, sort of making a funnel down to the burn area? That idea always made sense to me as well, but I have not heard about many people doing it that way. There maybe a good reason not to do that, but I was just wondering if it made sense and would work.

[matt walker]

Nice, glad it's working. Guy, the reason not to funnel is that by doing that you will have slower intake air velocity at the wider point, so flames/smoke are more likely to be able to escape. You want the air pulling down hard at the mouth of the feed, widening it works against that function.