Rob and Willi,
Here are some ideas behind the round oven deisgn. I'm not Italians and I don't play one on TV
, but I live here and spend most of my time with oven producers, pizzeria owners, tool producers, flour mills, etc. It's a of fun, and they really do a great job of brick ovens here.
1. The Round Oven design heats up much faster than the barrel vault oven -- less than an hour, compared with 2-3 hours or more for the heavier oven. The round dome is self-standing (ala the Duomo in Florence), so it does not need a lot of concrete clapping to hold it together. The barrel vault has a great deal of outward thrust, and needs a lot of concrete for buttressing. The round oven is lighter and depending on the material, will heat in an hour (or less depending on the type). Modern refractory ovens are designed with speed in mind, and heat up in about 40 minutes (not much longer than Kingsford). The barrel vault oven burns more wood (which isn't good for the environment or your pocketbook). For many, the heat up time is the difference between using my oven after work, or not. Round oven owners use their ovens a couple of times a week, and I know barrel vault oven owners that never fire their ovens.
2. The Round Oven can reach high Pizza Heat. Pizza should cook at around 700F, even higher. The round oven can reach and hold that heat, cooking pizza for long periods of time. The heavier oven has real trouble reaching and holding those high temperatures. The problem with too much thermal mass is that the heat from your fire has to heat the entire mass. That means that heat is continually moving away from the inside of you oven, where you want it for cooking, toward the outer edge of the thermal mass. That continues to happen until the entire mass is heated, which can take a very, very long time.
3. The Round Oven is designed for fire-in-the-oven cooking and pizza. With a round oven you have room for your fire on one side, and food/pizza on the other side and in the back. It's all reachable. With a 32x36 rectangular oven, there isn't a good place for the fire. If you put it on one side, you have very little room for food on the other side, and you cannot access the back. If you put the fire in the back, the heat and flame does not reflect to the front of the oven. A 35" round gives you much more usable space than a 32x36. For all the effort you are going to be putting into installing a wood-fired oven, a 32x36 rectangular oven is a one-pizza oven -- which is a shame.
4. The Round Oven cooks more evenly. The round, spherical dome does a better job of bouncing heat evenly on the cooking floor. You can cook pizza everywhere (or roasts and veggies) in the oven, and it cooks evenly. That is how the high volume pizzerias cook all those pizzas. The rectangular oven has a barrel vault, which gives you hot and cool spots, depending where the fire it.
There are also little things, like clean up.
The downside is that a pizza oven can only bake around 20-30 loaves of bread from a single firing, not 75. But for a home oven, that works for me. I make more bread than we could ever eat, and I give lots away.
There are about a million pizza ovens in Italy, and they are all round. I also think it is interesting that there is a lot of wood-fired oven bread in Italy (Pane Cotta a Legna), which is baked in large commercial brick bread ovens -- which are rectangular barrel vault oven. I think the idea is that there are two basic oven designs: pizza oven and bread ovens, and you need to think about how you want to use your oven.