Thanks Glenn, I'm beginning to realize that.
Would you recommend a 6x6 inch firebox and riser.
Also, I'm glad to hear that cob is safe for this application. I'll go for it. I hope you mean cob with straw since I already intend to use it for insulation.
I want to use cardboard as forms around the oven box.
Finally, should the fire box be centered under the oven arrangement? Or any will location (frontish) do? And, how high for the riser?
Thanks in advance.