The efficiency and energy savings from using a steam oven result from the greatly reduced cooking time as compared to using a conventional oven. Roasting a large chicken in a steam oven takes about 20 minutes as compared to two hours in a conventional oven. The overall heating element wattage in a steam oven also is less than for the elements in a conventional oven.
There are additional energy savings because the entire meal (meat, vegetables, and potatoes) can be made in the steam oven without the need for using separate pots on the stovetop. Stovetop cooking is particularly energy inefficient because much of the heat never gets to the food. Instead, it escapes around the sides of the pot into the room air.
Since steam cooking at home is relatively new, most people don't know how to cook with it. Most of the new steam ovens have a menu of foods from which you select. The oven determines the proper cooking time and settings. Some of them, such as Miele's models, have hundreds of food items stored in memory and combinations can be selected.
If you are planning to have fish, spinach and potatoes, select the three items. The oven prompts you to place the potatoes in the oven. After 18 minutes, it prompts you to add the fish. After nine more minutes, it prompts you to add the spinach for the final three minutes.
For more versatility, combination steam/convection ovens can cook even faster with both, or you can use each separately. For more browning and fat removal from foods, models that use superheated steam are available.