Restaurants that want to create a cozy, home on the range atmosphere can display their prepared soups in a kettle. These are just another type food warmer but with an outer body designed like a soup kettle that was used on pioneer campfires. However, these kettles plug in, require an insert and cover and probably should not be put in a fire. Soup kettles are designed to fit a specific size of food insert, usually 7, 10 or 22 quart sizes. These inserts are required, because the kettle cavity itself is not an approved food contact surface. The inserts are usually included with the unit, but if it is not, any standard size round insert will suffice.
Keeping the lid on the kettle will help reduce heat loss. The type of cover you want is generally a matter of preference. However, hinged lids are highly desirable because you simply open the lid and dish out the soup, rather than having to take the lid off and find some place to set it then remembering to put it back on afterwards.