Double Chamber Cob Oven 2.0
We’ve had the pleasure of using many different cob ovens, and perfecting our baking technique in our original, chimney-less oven in our yard in Calgary. If the volume of wood is carefully monitored, it is pretty smokeless, most of the time. But we are who we are, and we wanted to see if we could make an even better oven. So based on the work of some of our colleagues in the world of rocket mass heaters, we’ve built a few double chamber cob ovens. This design includes the addition of a smoke chamber, chimney, and utilizes a burn door. At the bottom of the burn door there is a cut out which matches the size of the chimney. This allows for controlled, even air exchange, while the smoke chamber encourages more complete combustion. After all, smoke is just unburned particulate. This design was to be the perfect marriage between the pyromaniac and the bread lover, or at least that was the plan. The diagram below should help to clarify the layout:
Assessment of Original Double Chamber Design
This version of ‘double chamber’ cob oven design is really based around an efficient, clean, wood fire. And at that, it absolutely excelled. We had our original double chamber oven for almost a year, and were thrilled to be able to throw a fire in, heat up the oven pretty quickly, and watch the chimney with joy as little to no smoke exited out the top. It has also preformed well under very windy conditions.
This oven was designed by an enthusiastic fire nerd, that much is clear. The burn performance is a great success. It seems, however, the needs of the bread baker (or pizza maker) were not equally considered. After a year of use, we came to the conclusion it was just too big, the interior dome height too tall, to really preform well for baking. And because of the extra size, probably used more wood than was really necessary. While it sure burnt a nice fire, it was rather disappointing to have delicious wood fired bread with a pale crust on top. Picky you say? Perhaps.
Our standards are high of course, but we really are committed to building the best ovens possible, and we think that means taking care to have a clean fire, as well as being able to eat the best food.
Double Chamber Version 1: Demolition!
At the beginning of May 2015, we actually took down our oven. This was a shockingly difficult task. Physically, the oven was incredibly strong (a good sign!), and it took way more work than expected to knock down. It was also hard to say goodbye to that lump of mud that had so much love put into it. But life goes on.
One of the great things about natural building is the ability for these materials to adapt and transform, so we’ve been re-hydrating the crumbling remains and making adobe bricks. There is also something really fantastic to be learned by taking something apart. It is a unique opportunity to dissect and inspect, and really understand.
Double Chamber Version 2.0 Rises From the Ashes
The next day, we hosted a wonderful workshop, full of dedicated students who joined us on this journey to a better oven. This time, we created our own design based on the more traditional proportions found in chimney-less cob ovens, including lowering the interior height of the main bake chamber. For those of you who have taken one of our workshops, you’ll be able to surmise that we also had to adjust the height of the archways, as well as the height of the smoke chamber and chimney to maintain that excellent, ancient, magical, highly effective, ratio of dome height to door height.
For the first week and a half the new oven was built, I found myself wandering down to gaze at it’s oh-so-satisfying shape, and impatiently sticking my head inside to see how dry the walls were. I started a few small fires, and watched as the last of the water turned to steam, and evaporated. After two weeks, it was time for the Phoenix to rise.
Double Chamber Version 2.0: Success!
We are happy to report that our design adjustments have yielded the results we predicted. The burn efficiency is still excellent, it is still very easy to light, and we are thrilled with the still smoke-less results, and it uses less wood that the previous version. We are also thrilled with the major improvements in baking and cooking. In the end, we also used way less cob, which is a side benefit means this design also saved in material, time and labour.