Minimum size for a castable WFO dome?

[Jumbalaya]

I have been planning a build and I have been shrinking the planned size of the castable dome in order to reduce the width of the stand and weight. I also am moving away from using a fitness ball to using a sand mold. Can someone please comment on the minimum size internal diameter that would be acceptable for cooking one 10-12" pizza at a time? I see some small commercial examples but i'm not sure what the drawbacks are. I found the post on the 600mm cast oven and it looks great but there is no follow up on the oven's performance.
Thx,
J

[Toomulla]

In my opinion 600 is a bit small, a small oven will heat quickly but with an active fire in half the oven it will be awkward coking a 300 diameter pizza at the same time. But if that is all the space you have better a small oven well insulated then a larger oven poorly insulated. In that size I would not bother with an entry structure or vent just the arched doorway provided the smoke is not an issue in the immediate area

[david s]

My oven is 540 mm in diam and there are times i wish it were larger, although there are probably many more that I'm glad it's small. Remember that the fuel consumption is relative to the volume of the oven chamber so a small oven is far more fuel efficient. If you increase the diameter of the oven by just 20% then the chamber volume is increased by around 70%. This also of course means that the larger oven will be massively heavier and dearer with only a small gain in internal size.Regarding heat up you would think that a smaller oven would heat faster. In most cases this is not so because it is the relationship between the wall thickness and the chamber volume and consequently the size of the fire it can contain, which determines how quickly the oven will heat up. My oven has 50 mm wall thickness but still takes an hour and a half to get to pizza temp, two hours if I'm doing a big party. Most oven owners only cook one pizza at a time because it takes longer to prep a pizza than to cook one.
I sometimes use an L shaped piece of stainless around 150 mm wide, placed to one side. If the live fire is contained in it then the pizza base nearest to the fire is protected from burning and I still have 490 mm of oven width, plenty for a 30 cm (12") pizza. I usually cook 9" pizzas though because it's easier to make and handle the bases that size.The height of the oven door can be a restricting factor for a small oven when used for roasting. Mine will just fit a 5 Kg turkey, a bigger bird wouldl be too tall to fit through the door.
I regularly cook a loaf of bread and a couple of baguettes (how much bread can a family eat in a day), firing the oven for one hour exactly from light up and using surprisingly little wood. You couldn't do that with a large oven. Likewise you probably wouldn't bother to fire up a larger oven to only cook two or three pizzas, but we do frequently.

[Jumbalaya]

Great thanks for the advice!