Troubleshooting fire maintenance

[etheil]

Hello all,

First, I want to thank everyone within these forums for the invaluable information you all contribute. I was helped immensely and almost exclusively by the information here while building my oven over the summer...I should have followed it more closely, which is a perfect segway.

I'm having problems with heat management, specifically, keeping a fire going after the initial firing. What I'm having trouble with is determining why this is happening. I was able to create some large fires at the end of the summer, but because of the moisture within the oven, was not able to get it hot enough. Now that it's winter and the oven is fully cured (I've fired it close to 30 times) the problem seems to be moisture within the wood. I've become an effective smoke signaler rather than a pizza maker.

Another problem is that I didn't use forms while building the dome, so the dome height is 21" with a 36" floor. The opening is 18"x12" with a flu of 5 1/2" x 11" and 36" high.

What's happening is that I fire the oven and then move the burning logs and coals to the side. Once that's done, I'll throw another log on the coals (I'm using the "wrist size" pieces) and from there struggle to keep the fire going.

So my question is, what types of things should I be looking at to determine what the problem might be? What types of troubleshooting techniques can I employ to figure out if it's dome height, flu size, wood moisture or something else.

Thanks,

Eric

[Wiley]

Re: Troubleshooting fire maintenance

Eric,
The first thing that comes to mind is the wood you are adding isn't dry enough. I would suggest an experiment: After you are done "smoke signaling" rake out the remaining ashes and coals and once the WFO has dropped to 500F fill it with wood. Leave the door ever so slightly ajar so that the moisture driven off has a place to escape up the chimney. When completely cool close her up until the next firing. Then remove the wood and load for the firing. If the wood doesn't burst into flames within a few moments of being placed on the coals then I will be surprised.

Keeping the fire going after the oven is up to temp should be no problem with dry wood. With my WFO I have little problem filling the oven with a great deal more wood than a complete firing takes. So even with a slightly smaller oven I expect you should be able to have more than enough absolutely dry for your next extended pizza bake.

Hope this helps,
Wiley

[Neil2]

Re: Troubleshooting fire maintenance

"The opening is 18"x12""

I assume it is 18 wide by 12 high.

Your door opening should be 21 * .63 = 13 1/4 inches high.

The door height to dome height is quite critical. If your door is 12 inches high it is too low. Your fire is "smothering" before complete combustion. Can you cut into the lintel ? Post a picture of your opening.

[Wiley]

Re: Troubleshooting fire maintenance

Neil2 is absolutely correct, my bad.

That being said, if cutting the lintel/arch transition between interior and chimney is not doable, another possiblity might be to raise the center area of the WFO by laying a single thickness of splits. Start back from the entrance something like 6 or 8 inches and don't bother to cut to fit exactly at the ends (at least for the experiment). If that does the trick move the front edge of the splits forward until it starts causing problems, then cut and fit the new interior hearth. The math: 21"-1.25"= 19.75"x .63 = 12.44" so you are still not a perfect 63% however, it might work (the 63% being the sweet spot).

Working with a step won't be as nice as a smooth transition (especially one of 1 1/4 inches) but perhaps more viable solution if cutting the lintel/arch is not a viable solution. Beyond that solutions probably get to be something you really don't want to do (tear down and build again).

And a quick question out of curiosity: When you say "initial firing" did/do you manage to get the ceiling to "clear"?

Bests,
Wiley

[etheil]

Re: Troubleshooting fire maintenance

Neil and Wiley,

Thanks for the responses. I've attached an image of the oven (it's an older photo.) The intention was to build it to 18", but, well...damn it all! I can get the ceiling to clear, but the sides near the floor of the oven are difficult. I've been able to clear the entire thing, but it was over the summer and I think I was dealing with dry wood and so was able to get much more heat generated.

I've been wondering if it's possible to lower the dome height by adding and layering splits to the top. Would that be too much weight? Is my only option to raise the floor?

Also, are you suggesting to cut into the lintel on the oven side of the flu or would the cut need to happen throughout. I did not build an arch and so I don't think I can cut into it because of the angle iron.

Eric

[dmun]

Re: Troubleshooting fire maintenance

Looking at your picture, I see the oven is sitting on a couple of inches of refractory insulation board, but the dome seems just to be covered by just a bit of concrete (I can see brick shapes through the layer). You say it's an old photo, was it taken before you insulated the dome?

Exposed domes, no matter what they are covered with, are prone to getting wet. I'm wondering if you are dealing with a wet insulation problem. This sort of thing would be worse in the wet winter than the dry summer.

[david s]

Re: Troubleshooting fire maintenance

If there is a ring of carbon around the bottom of the dome as you describe, it is a sign that the oven is still wet down there. The remedy is more fires.

[mklingles]

Re: Troubleshooting fire maintenance

you don't indicate how much wood or how long you are firing the oven for.

[etheil]

Re: Troubleshooting fire maintenance

The photo was taken before I put on the 3" of blanket insulation and vermiculite/cement layers. The ring of carbon starts about six inches above the floor and the last time it completely cleared was before I put the verm/concrete layer on the oven (that layer seems to have added a lot of moisture to the oven and prevented it from effectively clearing.) I normally fire the oven for about 2 hours and go through about 10-12 pieces of wood.

Has anyone ever had to lower their dome? Would additional firebrick splits placed in the dome, in an attempt to create a lower curved surface, be advisable?

Thanks,

Eric

[david s]

Re: Troubleshooting fire maintenance

The vermicrete layer adds lots of water to the oven. It is advisable to cure your oven before you stucco the outside, presuming you are doing an igloo. The curing at this stage makes the water removal easier. I don't think you need to alter the design, just keep firing and the moisture should eventually find it's way out. From my experience it takes around 10 firings to remove it all. You should notice an improvement as it dries. Any heavy rain on your oven will slow this process.

[Neil2]

Re: Troubleshooting fire maintenance

Before you lower the dome (which may be a tricky process), why not do a temporary floor raising as Wiley suggests ?

This will give you definitive proof on whether or not the door height to dome height ratio is at the root of your problem.

[shuboyje]

Re: Troubleshooting fire maintenance

Personally before doing and modifications I would get some scrap metal and build a simple draft door like in the illustration I made. There is a ton of turbulence in the vent area of a oven due to the exiting exhaust and the incoming air hitting each other and mixing. By dividing the two airflows with a door like I show you will supercharge the air flow. If it's an airflow problem this will fix it and then you will know and can decided on a permanent fix that doesn't block the door.

That said I personally don't feel it is an air flow issue.

[etheil]

Re: Troubleshooting fire maintenance

It sounds like I need to relax a bit and just keep firing the oven to clear the moisture from the vermiculite layer. There has been a marked difference between having fired the oven the day before adding that layer and the performance of the oven since.

Thanks so much to everyone for your input.

Eric

[DrakeRemoray]

Re: Troubleshooting fire maintenance

Hey Eric,
What kind of wood are you burning? I have had good luck with Oak from Rocky Mountain Firewood on Iliff. To me it sounds like your wood is just not dry.

[etheil]

Re: Troubleshooting fire maintenance

Drake,

I'm burning oak from Rocky Mountain Firewood (not the oak they get from new mexico, the barked oaked, but the stuff they get from Kansas I think.) It wasn't until my last visit there about two weeks ago that I found out how they stack those piles. All of the older wood is to the back of the pile. I was usually starting at the front and working my way back. That would explain a lot.

Eric