The Fresh Loaf

A Community of Amateur Bakers and Artisan Bread Enthusiasts.

WFO (head slap) (big head slap)

Edouard's picture

WFO (head slap) (big head slap)

So, I was cleaning in the living room yesterday when my interior wood stove caught my eye. Cast iron, good fire brick interior ... but old, and outdated. Not at all EPA certified. It's a cube of cast iron with a door and a flue and rudimentary controls. I keep it in the house just in case civilization takes a powder for longer than a month. Then I get this shiver ...

.... baking bread. And it hits me like a thunderclap, there are lots of older, non-EPA certified wood stoves being scrapped these days. The penny-trader classified paper out this way must have two free giveaway stoves each week (as people get rid of them). I am definitely going to give serious thought to building another WFO ... pretty much the same way I did last Summer, but this time watch for a classic cube shaped cast iron stove being given away, set it in and on a rammed earth pier, surround it with refractory sand and then pretty much cob-build out as before. 

Level off the interior with new firebrick up to the door lip and shazzam ... an oven that will hold heat like crazy, cast iron door, a good flue, old world reliability ... you see my point? The baking 'void' won't be the size of fancy Italian kit stoves, but hey ... despite Kiko Denzer's admonition to bake a lot of bread every time you fire up, it's just two of us and I only need one loaf at a time in the oven. 

The sand, btw, is to moderate thermal shock between the cast iron and surrounding clay/cob mass. 

I feel brilliant. Now, somebody tell me Why This Won't Work ....

Mini Oven's picture
Mini Oven

Sounds like a worthy project. 

Brainstorming.... the flue could be too open.  Find a way to control and trap in the heat so it doesn't rush out when the door is opened.    I'd try burying it in the sand for a trial run.  There might be a reason wood fire baking ovens don't have iron inserts.   One reason I can think of is the melting point of iron which is quite high but if the oven was really stoked up, you might reach it when it is insulated.  So be careful not to get it too hot.  Have your high temp thermo gun ready!   Brick lined inside sounds good to me.  Are you going to put a brick bottom in the stove chamber?


ClimbHi's picture

Most wood stoves, fireplaces, etc. are designed to move the smoke out of the fire chamber as quickly as possible. This means the flue pipe is integral to the fire chamber. WFOs, on the other hand, are meant to retain the heat (and thus, smoke) for as long a possible so the oven walls/roof/floor get hotter faster. To accomplish this, a well-designed WFO has a door that is about 2/3 the height of the oven ceiling, and the flue is outside the door.

You could use the stove as a fire chamber - no reason you couldn't. But to make it efficient, you'd probably want to redesign the venting as described, thus increasing the heat retention efficiency.

Pittsburgh, PA

pmccool's picture

I'd be concerned about two things. 

First, although you aren't likely to achieve temperatures that would melt the iron (which would be in the neighborhood of 1100C), your usage pattern will probably lead to faster oxidation of the iron components than would ever be experienced by the original stove in its indoor location.  That's mainly because the usage will be intermittent, with opportunities for moisture to collect on the iron surfaces between firings.

Which is also the root of my second concern: how to protect the iron parts from moisture.  I'm too ignorant of the cob's abilities to shed moisture to know if this is a big deal, or something minor.  At a minimum, you'll want a cap on your stovepipe to keep rain or snow out.

I don't see either of these concerns as a show-stopper.  Just something to think about as you work your way through the design considerations.


ehanner's picture

One of the benefits of a WFO is that the heat is stored in the roof as well as the floor. If I am understanding what you propose, you will be missing the brick roof and the majority of radiant heat will be from the floor. For even baking you need radiant heat from the roof.

Now, if you built an angle iron frame to hold fire bricks on legs just below the roof of the cube, I think you would have it. Essentially a table with slats to support the bricks. I would use the heaviest material available to offset the high temperatures and weight of the bricks. You wouldn't want the slats to sag. The top should come off the cube for easy access, yes?

Sounds like a fun way to create a nice wood oven.


crazyknitter's picture

You definitely have me intrigued.   I am interested to know if this would work.



Edouard's picture

Okay ... there's more to the story, of course.

You've seen my finished earth oven. Big sucker and it works fine. But it doesn't retain high levels of heat. Firing it goes to about 700F then as I 'soak' it, it drops off to about 400F, then 350F and moderates within the hour to about 250F. It's closed up pretty tight but not as tight as a custom made door would be, and since only the floor is fire brick, the walls are all clay with a ton of clay mass behind them but still ... clay. 

Now the thing works fine for the two of us. It would be unsuitable for a commercial operation. But I didn't build it to be. It was a first run trial at building a WFO. A pretty doggone successful. But ... 

... heat retention. I'm looking at the old woodstove, a cube of sheet steel and cast iron on a pedestal with a dang fine door that seals tightly and it occurred to me that woodstoves are made to retain heat, and to seal tightly, and burn cleanly. 

So .. I says to myself ... why not take an old cast off cast iron wood stove, give it a good cleaning, layer the interior with refractory sand so that the fire bricks would be level with the door ... place the thing on a bed of gravel and sand upon whatever foundation works to isolate the heat and to trap it as much as feasible (mine sits on a two inch thick slab of red navaho sandstone) ... then enclose the stove with adobe-cob leaving a layer of gravel and sand around it to moderate the heat retention and heat loss ... and voila! Seems like that ought to be a dandy way to go for superior heat retention. 

That wood stove can be fired so hot, the wood 'comfort-handle' on the door handle charred and burned ten years ago ... this thing gets HOT. And will retain heat most of the night. Get up in the morning after a full load of fuel the evening before and the flue temp is still around 350F. That's what wood stoves are meant to do. 

They also do a good job of burning off noxious and toxic gases, at least a properly maintained stove will. 

I can't see a downside to this. Now ... if I could wave a check book at my desires and solve them, I'd just order up a refractory qualified Italian gas fired oven and be done with it, but I have to think through what can be done vs. what I can pay for. This is a scrounger's idea.

Also, this might be a heckuva way to build a two chamber oven ... fire below in one chamber and the oven above in a second chamber being heated to temp by the hot gases passing through on their way to the flue. See   

crazyknitter's picture

I think that sounds good.  Why not?  Go for it!  If anything, it will be a wonderful learning experience.

Edouard's picture

One thing is certain ... having just proved it this winter ... the next batch of cob-adobe I make to build an oven will have a decent admixture of ash left over from firing my current oven and my barbecue. 

I know about 'fly-ash' ... the ash-remnants of coal-fired power plants ... but the local plant that makes tons and tons of fly ash is not allowed by the EPA, Colorado Department of the Public Health and Environment and the power company's own legal and environment al staff ... at least not allowed to 'private individuals' ... companies and corporations, sure ... but not little old me. Even though they're hauling tons of the stuff up into a mountain and dumping it by tandem dump every 15 minutes 24/7. 

Anyway ... the ash remnants from my fires mixed with clay and aggregate is making an adobe/cob mix that seems indestructible and quite adherent. 

In fact, much better than adding a taste of Portland cement.