[Cob] Re: rumford fireplace

[ocean]

OK, Amanda has some things correct about the cob oven.  The chimney is 
needed if the oven is indoors, certainly.  Outdoors, it's optional - 
yes there will be some soot around the door if you don't have a 
chimney.  Even though we do have a chimney, some smoke will escape out 
the door resulting in a soot "patina" on the front of Maya's face.

How long you fire it depends on what you're cooking!  If you want to do 
pizzas or grilling (as we do) we keep a fire in the oven all day, so 
the deck is around 650°F.  We take the fire/coals out of the oven when 
we cook our artisan bread, and just fire the oven 450-500°F.  Because 
the oven is well insulated and we seal it at night with a door, it is 
around 350-400°F when we arrive the next morning, which would be 
perfect for roasting a turkey (Happy Thanksgiving!)

However, our cob oven burns very clean - the high temperature of the 
oven "bakes" the wood completely dry, so it burns near 100% leaving 
very little ash and no smoke(!)  The central core thermal clay layer is 
surrounded by a foot of pumice, thus good insulation helping contain 
the combustion heat.

The Kiva's Rumford cob fireplace also burns very clean, lots of radiant 
heat and very little smoke or ash.  Of course, the most efficient wood 
fire I've seen is in Ianto's rocket stove design, where a super 
insulated firebox results in a 2000°F burn - no ash except a fine 
mineral dust, and no smoke discharged, just steam similar to a laundry 
vent.

Yes, I would advise buying Kiko's book, if you want to cook with cob 
and fire.  But if you want to heat with wood and fire, buy the Cob 
Cottage Company's new booklet on the Rocket Stove (much more efficient 
than even the Rumford).

Ocean Liff-Anderson
_____

Steward, Ahimsa Sanctuary  http://www.peacemaking.org
Proprietor, Intaba's Kitchen  http://www.intabas.com


On Nov 20, 2005, at 6:23 AM, Amanda Peck wrote:

>
> I've gathered that the difference between an horno with a chimney and 
> one without is that the one without puts soot above the door and the 
> one with puts the soot out of sight in the chimney.  If it were 
> indoors, then a chimney all the way out the roof would be good.
>
> See Kiko Denzer's book.  Better yet, buy it.
>
> They're not particularly efficient at burning, I've gathered.  Ocean 
> may have some other thoughts, since he's familiar with a wood-fired 
> pizza ovens in a commercial setting--and Intaba's may be in use long 
> enough in a day to have thoroughly fired the clay, if they are the cob 
> horno type.   And the whole point of the fire is to get the oven up to 
> 500-600 degrees F.  Then you take the coals out.
>
> "My family" in Mexico did one burn a week in their giant outdoor oven, 
> baked all day with it, finally putting in a giant (4-6 feet long, 
> around a foot in diameter) tamale (called a sacahuil) to cook all 
> night.  It was nicely done and still warm the next morning when they 
> took it up to the weekly market to sell in portions. A little 18" home 
> oven almost certainly won't hold the heat that long.
>
> And lots of people report cracks in their ovens.  They're not that bad 
> to repair, if the cracks bothers them.   And the dome shape would mean 
> that if it failed enough to collapse it would fall in on itself.
>
> by contrast, the Rumford fireplaces, probably even the outdoor ones, 
> get hot enough to keep the soot off the back.  They're intended to 
> warm people, to be kept with a good-sized fire in them all evening.  
> And if they fail enough to fall down, that big and as tall as possible 
> chimney on top of the thin short to back fireplace is going to go 
> somewhere, most likely forward or back.
>
> The Buckley Rumford site mentions that trying to make a Rumford 
> without using stone or regular brick instead of fire brick for the 
> inside veneer and floor often leads to cracks and spalling, that 
> historic fireplaces show signs of damage.  He sells plans, not 
> firebrick (those may come from the wood-stove store).  But he does 
> have to promise that fireplaces built with his plans will hold up.
>
> But if you're really trying to be all home-grown natural, you MIGHT be 
> able to just do the floor and back.  (don't try it with the burn 
> tunnel in a cob bench, though)
> ....................
>
> Susan wrote:
>
> Thanks, Charmaine- I've been thinking about an horno with a 
> chimney/vent for cleaner burning (another project.)  Most of the cob 
> oven pictures I've seen have only the door opening.
>
> As for the Rumford.....it needs a specific shape and size of throat 
> and damper.   Those parts can be ordered from Superior clay, and the 
> specs and instructions are on the rumford.com website.  Now, instead 
> of firebrick, can the fireplace itself be made of cob?  What's the 
> difference between a cob oven and a cob fireplace?
>
> To set your minds at rest, this experiment will be for an outdoor 
> fireplace.  I won't be building a residential fireplace for at least 
> two years.
> -susan
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