posted 9 years ago
I'm not an authority on wood-fired ovens (I have built one so far), but I think the first thing to figure out would be the usage pattern you need. A traditional oven has the fire inside, heats up, the fire is raked out and baking begins, with fast foods to start and slow foods later. If you want more even usage, a rocket-fired oven might be better, as it can be kept at relatively constant temps all day after warming up.
I don't know the fuel consumption differences between styles, but I tend to think you could use less wood with a rocket oven. Mine is an L-tube beneath the oven floor which splits into five channels (more than necessary, I found) and comes up around the edges of the chamber. I have the equivalent of two bricks thickness of floor between the fire channels and top surface; it would heat up much faster with only one brick thickness. I have a chimney above the door opening which draws nicely, and if it were inside a building and going high enough to clear the roof, it could probably keep negative pressure at the door so hot gases (no smoke after the first five minutes of firing) don't come out when the door is open.
48" doesn't sound too big for a cob dome as long as it is well supported. If there is a tension ring around the outside base to prevent any spreading, the dome might even have good earthquake resistance.