Steel Dome Oven

[Wiley]

I've taken several photos of the intermediate steps but figure unless the oven works they are not really that valuable. So today I assembled the pieces I have built on the driveway in front of my home and had a test fire.

So lots of things were "mock-up", the bricks on the hearth are old red bricks and in order to insure some sort of air-tightness I packed sand around the outside of the dome itself. The chimney was something I found at the recycle center (see where I shop :-)

I am including a photo of the three pieces before assembly. Also I would like to know (even though the photo doesn't show it) I did get a small wisp of smoke out the front, is that common or do I need to consider rebuilding my transition piece... in this case the hoop band that connects the chimney to he FWO? Thoughts and opinions welcomed.

Wiley

[gjbingham]

Wiley,
Very cool. A one in a million oven. I'd consider adding about 4 inches of cladding or some type of heat sink outside the dome to increase your thermal mass. That should help retain heat much better than just the metal dome alone. Insulation outside of that, a finish, and you're done!

[Wiley]

Thank you for the kind words, George. Yes, the plan is to cover the dome with aluminum foil and then 3-4" of basalt concrete (basalt 1/4 minus mixed with calcium aluminate cement) scored deeply so the expansion cracks will be somewhat controlled. The a Frax blanket and vermicrete and stucco.
I'm a bit concerned about the small amount of smoke I'm getting out the front. Is a small amount normal? I mean I see photos of ovens with significant soot staining and don't know how my loss thru the front compares (due to small test fire) a real fire. Any thoughts? Maybe I'll try a much larger fire tomorrow.
Thanks,
Wiley
Oh, and here's a picture of me :-)

[Frances]

I think a bit of smoke, specially while the fire is starting up, can be considered normal.... well, I know my oven spills quite a lot of smoke to begin with. Less would be better...

Your idea of building a larger fire sounds like a good way to go. Then you can decide whether you can live with the amount of smoke or not.

As long as the smoke stops pouring out of the front once the fire gets going properly you should be fine.

[dmun]

I think another length of the chimney pipe would be more useful than a re-designed transition. Remember; this is all outdoors, where drafts push smoke around, and you don't have the temperature difference between outside and inside that drives fireplace draft. A whiff of smoke on startup is normal, but smoke pouring out once the fire is going strongly is not.

[brokencookie]

Your smoke will always go from hot to cold. The larger the difference in temperature the better the draw. Somebody posted a spreadsheet that calculates chimney draw on the forum that you can use to check this. So.. Once you insulate, your oven will run hotter, creating a larger difference between the oven chamber and the outside air. Additional chimney height can also help.

Bruce

[Wiley]

Thanks everyone for your imput.

dmun: we added an extra short (36") piece later during the trial and did not detect any difference. We were still getting a slight amount of smoke out the front. Of course things had warmed up a bit so it wasn't a proper test although it was still only a small fire. I would like to have an igloo rather than a gable framed FWO and so keeping the chimney as short as practical is desireable, supporting 6 ft of chimney presents its own problems.

Thanks Bruce I looked into the flow rate calculator unfortunately there are so many variables such as chimney throat shape that for me experimenting seemed the easiest answer.

One thing that crossed my mind during our morning walk. (we do 2 1/2 miles every morning sun, rain, snow, whatever the weather). When I constructed the ring that holds the chimney in place on the top of the transition piece I deliberately left about a 3/16" supporting lip all around the inside. That 3/16" x 18 3/4+ inches circumference actually reduces my X-sectional flue area by about 3 1/2 square inches. The 6" chimney X-section is nominally 28.27 sq inches, that support is reducing that to less than 25 inches. I should reduce the support ring to three small protusions and so recover a majority the lost area. It's an easy enough thing to modify. If I get 3 sq inches back I'll be increasing my present flue X-section by about 12%.

Here's a photo of the lip. Thoughts? Anyone see something I'm missing?

Thanks everyone, Wiley

[Wiley]

Well, I did the modification to remove the excess chimney pipe support and reassembled the unit. I also extended the chimney to 4ft. It rained last night and all this morning and so the ground was soaking.

I decided to build a second bigger fire, not a super raging fire as without the heat sink of the 3-4 inches of basalt concrete I could easily reach 1000+ F in a single spot and perhaps cause myself some unwanted problems. As it was with this little fire I got the top of the dome to 625F within about 15 minutes. The smoke problem seems to be resolved. Here's a photo taken with the fire going.

Wiley

[asudavew]

I'm really enjoying this thread.
Great design.
I have to agree with George about the cladding.

thanks for posting

Dave

[granvillearden]

Great Job. I am considering one like this myself.