I am interested in building a high temperature oven (similar to the Breville Pizzaiolo) to experiment with flatbreads and pizza.
Has anyone tried using a commercial griddle together with an inverted electric grill on top (some metalworking required:
Griddles are very cheap and typically go up to 300C, they heat up more quickly than an oven (especially when heated from the top as well). It would take forever to heat a baking stone in an oven to 300C, if it would reach that temperature at all.
A pizza oven has a floor temperature ~400C, but the stones have a far smaller heat conductivity, so a griddle with a cast iron, or better steel clad aluminum, plate might work just as well at 300C. Modernist Cuisine claims that a steel plate at 230C (450F) works similar to a ceramic oven bottom at 430C(800F) https://modernistcuisine.com/shop/baking-steel/ so the idea is not absurd.
Heating from the top is less of a challenge, a 1.5kW grill heating element will have enough power to heat a small space.
Is this a bad idea? Has anyone tried?
From an engineering standpoint, inverting something that was designed to be used "right side up" is dangerous.
It was designed taking into account the fact that convection heat _rises_, hence the insulation (even if it is just air space), which was at the bottom in normal orientation, and now at the top in inverted orientation, will likely be insufficient for the rising convection heat, and therefore the outer shell will receive more heat than what it was designed for. The shell enclosure (which was on the bottom, but now is the top) will char and possibly melt, if it is plastic. And will dangerously overheat if metal.
The reflector plate and enclosure is not designed to channel off (to direct) or vent rising hot convection air flow in a safe manner when inverted, neither by its shape, nor its material, nor its coating.
It's a safe bet to assume it was never tested in an inverted configuration.
Then consider the additional convection heat rising from the griddle, and you are asking for disaster.
There are good reasons why high temperature ovens, such as the Breville Pizzaiolo and the Turbo Chef, are very high in price.
Thank you for the thoughtful comments, I agree with the convection issue.
Just putting the grill on top is not enough, also the heat would leak to the sides. My plan was to build a square sheet metal box with ceramic insulation that fits on the griddle and put in the heater element into that box, no plastic and no electronics above the heater. Heater elements for ovens are very cheap and easy to hook up and they are designed to handle the temperature and just burn out safely if overheated.
I am just not sure it is worth the effort as far as temperature, heat conductivity from griddle plate etc. go, so I am very interested in hearing whether anyone else has any experience building their own ovens. Plenty of posts on wood-fired ovens, but very little on electrical ones with metal baking surfaces.