To chimney or not to chimney?

[limpopomark]

I'm being a little lazy and pasting this from my build thread, but I have a couple of questions about chimneys... I'm starting a clay/earth oven, 80cm internal diameter, and nt sure whether it needs a chimney or not. I'm planning to use the 63% of the internal height bit for the opening, if that helps, but...

I never intended to have a chimney; if I really ought to have one then I will. Pride says ''balls to chimneys'', as the folks here have all said I have to have one. That said, they all think i should be building with concrete, not mud and elephant do-do. So I'd like to hear pros and cons, really.

Second: Brick arch for the opening or not? I like the aesthetics of the pure dome, but am also sold on the protective qualities of a brick opening. What say you all?

Thanks folks, and please excuse my slackness,

mark

[cannyfradock]

Mark

A Clay/Cob oven is the only home built Wood-fired oven (pompeii and barell/Vault oven excluded) that can be built without an entrance arch or chimney.

My last Clay oven build.......

ukwoodfiredovenforum.proboards.com/index.cgi?board=ceovens&action=display&thread=599

....was built with an entrance archway and a chimney. I'm a bricklayer by trade so I found this the easiest way for me. It's about 50/50 with all other clay oven builds. The difference will be minimum in performance but the saving grace with an entrance arch means you get to keep your eye lashes and eyebrows after each firing!!!......

Terry

[limpopomark]

Cheers Terry - the decision is made: arch but no chimney. The more hair I can keep the better, and I am sure my (marginally) more full-head-of-haired boss will appreciate the decision, too.

mark

[Woody]

Hi All,

I am hoping to start a clay/cob oven this year (once the frost has gone!) and was wondering the same thing Mark.

Is it is okay to use normal house bricks when building the arch or should I use fire bricks due to the heat?

Also, should the mortar be special fire cement or similar?

Thanks,
Woody

[limpopomark]

Hi Woody

Based only on my own experience of house bricks and regular mortar... if using them, expect cracking of mortar along joints. My arch - mercifully - is standing and stable. Although one of the bricks has come free of it's mortar on one face, and slipped into the arch (maybe 5mm) it is held fast by the archand the integrity of the arch remains.

Not sure if firebricks and fire cement would really make any difference - the clay/cob will expand at a different rate to your bricks anyway, so cracks are pretty much guaranteed. It would seem that as ling as the ointegrity of each layer of your build remains, and the arch remains an arch, you still have a working oven. I think housebricks are already fired at higher temps than your oven will reach, so unless the bricks were already a little iffy they should be OK.

In short, I'd say its ok to go with regular bricks and mortar, but expect cracks - they can be repaired.

Re chimneys, i don't see any need to bother. It adds fiddliness to the build and also is another area where cracks can focus. Be sure to get the doorway height to internal height proportions to around that magical 63% mark and your fire will burn just fine.

I'm looking forward to what anyone else has to say, and to the pics of the build.

My overall impression of my first build is that I wish it was my second - I am sure a lot of the little niggles would have been sorted out!


Good luck,

mark

[cannyfradock]

I agree with Mark with all points except one.....if you're going to the trouble of building an arch, it's just as easy to leave a vent in the top of the arch when you're building it. You then have the option of popping a clay pot over the vent or s/s alu chimney or even try your hand at a brick chimney.

It will also help with the "draw" of the fire and deflect any smoke away from your face......and you get to keep your eye-brows...and lashes.

Terry

[Woody]

Thanks Terry and Mark that certainly gives me a couple of options to think about.

I am waiting for a break in the weather before I start the build.

In the meantime here’s a snap of the location...

Notice that the garden is raised so I have dug a hole where I plan to build a breeze block frame which will take the finished height approximately level with the land.

I am going to fill the block frame with sand and maybe wine bottles then laying the fire bricks on top.

Cheers, Woody.

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[limpopomark]

Terry's point about eyebrows and eyelashes is a good one - without a chimney you will get flames licking their way out of the arch - if you value your locks or use a lot of hairspray, get a chimney on the oven for sure.

As for the photo, all I can say is that these things weigh a lot - maybe half a tonne - so be sure that what ever it sits on can take the weight and isn't liable to sink & tip after heavy rain or otherwise subside. And try not to burn down those conifers!

The result will be all the better for the research so keep asking stuff. I've built one oven so am hardly an expert but the views of folks on here and elsewhere certainly helped shape the little oven we now have. And I love it.

Good luck, and have a good weekend

mark