Many sizes are available from table top units that hold 7 half size bun pans to units that hold up to 18 full size 18″ x 26″ pans. Some models have manual dial controls and others have digital controls.
The benefit of combos is that they may be used as convection steamers, or as convection ovens, or as a combination of the two, adding the speed of steaming to the browning and crusting available with high temperature air. Convection steamers cook very rapidly but do not brown the product. This is especially important with roasting meats. Ovens do a great job of colorizing the product but may dry them out, requiring basting, and take significantly longer to cook than a steamer. A combo might be used first in the morning to do baked products, like breads or deserts. After the baking is complete, the unit might be used as a combo unit to do the meat roasting. Finally, as serving time approaches, the unit might be used as a convection steamer to do ala carte steamed products, like vegetables.
There are numerous manufacturers of combo oven/steamers. The major differences are in overall size and capacity of the units and the control packages. Some have digital controls while others find manual controls easier to use and train on. Some manufacturers units are MUCH easier to descale. Some units have glass or solid stainless steel doors, condensate controls, cool down modes, interior lights, and meat probes. Probes allow the user to cook meats to a desired internal temperature, automatically. Some models of some manufacturers are stackable for increased versatility.
Available voltage and phase on electrical units, gas type on gas units, availability of water and drains is critical. You should have a good idea of the menu that will be cooked in these units so that you can specify the right size unit or combination of units. Floor drains should be located within 6 feet of unit.
Be careful with these specs. Some people believe that this unit can replace your existing ovens and steamers. Others believe these units to be a great third piece, to augment the ovens and steamers and to back up either piece and add additional volume capability. You would not want to eliminate the other pieces. You may want to be using the ovens for pizza while you are using the steamer or combo for steaming. You cannot use the combo to steam and bake simultaneously. If you purchase two combos you will have that versatility, but the purchase price may be too high. Combos can NOT be used to provide steam to adjacent direct steam kettles. This requires a pressure boiler, as is available with floor mounted steamers. Combos use atmospheric boilers, which cannot power anything else. Don’t forget, as with all steam equipment, water conditions are vitally important. Be sure to use a product that has a water treatment device available.