~38" build in Seattle

[boerwarrior]

Re: ~38" build in Seattle

Keep up the faith!

FWIW, I pulled my forms immediately after mortaring my arches (I have a total of 5 arches on my oven). My logic was that the arches are really self-supporting - and the mortar is under compressive force in the gaps. All my arches held fine - but then again I didn't bump them until they had set a little better!

[pluscwc]

Re: ~38" build in Seattle

Have made a bit of progress finally.

Finished the heat break (if you type it as one word, it autocorrects to heartbreak) with Inswool Pumpable and ceramic rope I got from McMaster Carr. I let it all cure for two weeks while I was waiting for chimney parts.

Lit some fires finally. Yesterday roasted some corn on a tuscan grill. Today roasted some volunteer cherry tomatoes with the heat following a curing fire. The tomatoes turned out great. I've seen the dome temp get up over 750 on the inside and 200 on the outside so I think I've driven the moisture off.

My problem is the draft isn't great. Even with 10 feet of 6" duratech piping, I get a fair bit of smoke out the front. I've been firing it with one of my arch forms blocking off the top of my entry, but I need to come up with a better solution.
Sorry for the lack of pictures, I'll try to take some more this week.
My problem is partly to do with having the 6" rather than 8" pipe. and partly that I built my entry only 9" deep in order to get the chimney to clear a roofline.

I can either tear apart the entry and rebuild it deeper or tack on another section of arch to make it deeper. I'm leaning toward the latter, combined with taking an angle grinder to the inside of the arch to improve the size of the smoke chamber. I have the space to make it deeper.

Glad to finally be firing. I really need to get my roof on before we have any more torrential downpours.

[pluscwc]

Re: ~38" build in Seattle

Oh, and I ordered some peels but UPS discovered the package was damaged after it got to my local sorting facility, so I'm still waiting for them to go back to the vendor and the vendor to ship replacements.

Grumble, grumble, grumble.

[deejayoh]

Re: ~38" build in Seattle

Your arch should be deep enough. Mines only about an inch deeper and it drafts just fine. I'd suspect your 6" flue is the problem. You really should have an 8" flue on that size oven.

[pluscwc]

Re: ~38" build in Seattle

Based on calculations for flow earlier I believed I'd be OK with the smaller chimney.

I feel like I have a choice between spending $1000 to put in an 8" chimney and trying to make it work with the chimney I have, which really only smokes badly at the beginning and end.

Any chance I could visit someone's oven in the Seattle area to experience the firing process? I want to know what it is supposed to be like, so I can judge if it's worth the cost to improve.

[deejayoh]

Re: ~38" build in Seattle

Well, I hear you on the cost. I think the duravent was the most expensive part of my whole oven. I am surprised there's not some sort of chinese knock-off - but they seem to be the only option.

Not sure about what the calculator says, I'm mostly going by my own experience and from watching what others have done. My oven is 39" and went with 8". I haven't had any significant smoke coming out the front. Maybe a little with a super smokey startup on a windy day - but never enough to stain the front.

That said, if it's not so bad that you think you can live with it - I'd do just that. You can put another ~2.5" inches on your arch with a decorative arch, which will probably solve your problems.

PM me if you'd like to check out my setup. I'm on QA.

edit: one more thought, it is probably smoking more now that it will later because it's curing. One more point for leaving it.

[GianniFocaccia]

Re: ~38" build in Seattle

FWIW, my 40"L flue is 7" for a 39" oven, and it works just fine. I'm wondering if your door size (11.5" x 19") is contributing to the draw. If your final ceiling height matches your 38" dome, your door works out to be just 60%, a tad on the low side, by my math.

[Gulf]

Re: ~38" build in Seattle

It may be too late, or too difficult, to change anything that you have already built. But, I would try a very simple, and also a very cheap trick, to train the smoke to go where it should. The trick is to preheat your flu, before you light the fire in your oven .

[Steellearning]

Re: ~38" build in Seattle

I had problems with smoke also. I found that if I start the fire with the top down method and used smaller wood to keep the fire hot, smoke was not a problem any more. The goal is to get the gases and smoke to combust before it leaves the oven. As the oven cures it gets easier to keep things hot enough..

[pluscwc]

Re: ~38" build in Seattle

Thanks for the ideas and support.

I fixed some obvious things and it worked a bit better most of the firing today. Still quite a bit of smoke out the front when the fire was smoky though.

Step 1 was switching from the random chunks of black walnut that I picked up to some big leaf maple that has been seasoned for 5 years. I also split it down to smaller pieces and added them gradually rather than building the fire and letting it go, following some of Steellearning's advice.

Step 2 was trying to restrict the oven throat a little. I measured the height, it's actually 12.25". I think having a more semicircular opening instead of straight walls and an elliptical top would channel the smoke a bit better. See picture with bricks jammed into the sides of the opening. This channeled the exhaust out under the chimney better.

The odd pattern of soot stains on the front are due to my having a plywood arch support blocking the opening during previous firings, it leaked more on the sides, so they got sootier.

Step 3 was following Gulf's advice even before I read it. I made a torch and held it in the chimney for a bit while the fire was getting going. I think this is even more important with a tall chimney, since I have to get a bigger mass of air to start moving.

All of those made things tolerable to me. I'll probably still try to open up the smoke chamber with an angle grinder.

Got part of the dome to clear. Cooked foccacia (no pics) and worked on seasoning a thrift store cast iron pan. Developed a full set of cracks in the dome, some of which are pictured below. Outside of dome was over 200 at the base, I forget the top number. The drawings in the crack picture are from my son and brother, who I encouraged to decorate the oven while it's still open.

[Greenman]

Re: ~38" build in Seattle

You can also use a blast door at start up and that helps direct the smoke up the flue during the startup. Need to use it with some care as it really excites the fire and you can get a lot of heat happening quickly and it is better to heat the thermal mass less furiously.

I use the blast door until things get going right and then use the heavy door offset in the entrance to keep the heat in the oven and smoke going the right way with the heat being applied to the oven a little more gently.

Worth a try, nothing to lose. It works well for me.