Why do we turn down the oven after introducing the bread?
It's commonplace to recommend turning down the temperature from 500 to 450 when the proofed loaf is put in the oven. Why do we do that? In a WFO, you don't do that, and I would expect that in a commercial deck oven you wouldn't either. Is it to simulate a stone hearth which might be hotter than the air in the oven? I don't think so.
I think turning the heat down is to prevent the top element from coming on when the door is opened, ice cubes inserted, and a few pounds of room temperature dough added. The stone adds thermal mass, but the oven thermostat isn't sensing the stone (which is probably masked from the sensor by the bread anyway), so the heating elements turn on at full blast to correct the temperature, and the top of the bread gets a lot hotter than 500 due to the red-hot element just inches away from it. Turning the temperature down is exactly the same as turning off the oven for a period of time, till the oven has reached equilibrium at the new set point. The bread bakes from the retained heat of the oven in that critical first minutes in the oven.
That is one reason that the cloche, the no-knead casserole, and Susan's pyrex bowl produce such good bread. No burning. The other (and probably the main) reason is that they trap the humidity of the bread as it heats and keep the outer layer of the bread gelatinized and prevent the slashes from hardening too soon. Without the cover, you need to turn the oven off for a bit to prevent burning.
Ovens have different cooling rates, just as they have different heating rates. My present oven is very well insulated, and I'm certain that old ovens cool off pretty quickly, so they would cook at a lower temperature than mine. I think more consistent results would be obtained by using a cover for the first part of the bake, and just baking at the desired temperature.
We 'over' heat the oven so that when you open the door to load the loaf and heat pours out, when you close it again it will be at the right temperture.
If the oven is at 450 and you open the door the temp will drop below 450. If you have the oven at 500, when you open the door and slide in the bread, the over temp will be at about 450 when you close it again.
A wood fired oven has considerably more mass to retain that heat than a standard kitchen oven so heat loss is less of an issue.
It's also important to not just pre-heat the air in the oven but to give that heat time to warm up the physical oven itself... which will also help with recovery from heat loss.
My 2 cents worth...
Robert
First off, it sounds like you bake in an electric oven. Not everyone does. For those of us baking in a gas oven, there is no upper heating element. So your explanation doesn't apply to us - who also, btw, turn down the oven temp after loading.
You are correct that WFOs and commercial ovens don't adjust temperature when loading dough. As you note, in the former, there's no turning down the temp, and in the latter, fully loading an oven will reduce the temperature by some degrees (as it will in WFOs that are fully loaded).
For home bakers, however, the explanation topslakr provided is spot on: once you open the oven door, you are decreasing the internal temperature substantially. So the better strategy is to heat the oven beyond what the recipe calls for, and then to reduce the heat after the bread is loaded.
Lary