The majority of us have tried different steaming techniques..professional steamers, ice cubes in the bottom of the oven, ice cubes in cast iron pan, spraying the loaves, spraying the oven walls, drip pans, pouring water into hot pans, pans with water heated during the preheat and combos of these techniques.
I have found that heating 1/4" hot water in a metal pan during the preheat gives me an oven full of steam by baking time, so much so that I have to be careful and keep my face away from the oven door when I open it to avoid getting a steam burn. Even after loading the oven, a few minutes later I see steam coming out the vent.
I recently tried the suggested method of pouring 3/4 cup hot water into a sheet pan that had been preheated with the oven. I thought even better was to use boiling water. Quite frankly, it seemed that I hardly had any steam compared to the way I had been doing it.
Does the temperature of the water poured into the pan make any difference? If I had used just hot water vs boiling would there have been more steam? It looked like it evaporated almost as fast as I poured it.
I do remember (I think) that someone said what was being produced was vapor not steam by most of these methods.
One caveat for all new bakers..If you have glass doors, be sure to cover with a dry towel when pouring water to avoid cracking the window.