Small electric water boilers are portable household appliances, used to prepare hot beverages or other food items. They may provide a reservoir of hot water to be kept at a fixed temperature or to allow tea to be steeped at a controlled temperature. They are manually filled with water every time hot water is desired.
An electric steam boiler is intended to produce steam for process industry or other uses, such as drying, heat treating, and others. These are generally permanently installed systems with connections to a water supply and piping to transport product steam to the point of use. In places where electric power is relatively low cost compared to fossil fuels, it may be economically practical to use an electric boiler for steam central heating. For example, in Winnipeg, Canada, during the Second World War, large central electric steam boilers were used for a district heating system, using surplus hydroelectric power. The intent was to conserve coal fuel for more critical wartime needs.
Electric boilers may rely on immersion heater resistance heating elements to heat water, or may use electric current passing directly through the water as an electrode boiler .