A boiler is a container in which a wash is heated to its boiling boiling point. The steam then travels to the column or lyne arm. The characteristics of a good boiler is that it made out of a material that is strong and will not corrode, such as copper or stainless steel, it has a fairly good height to width ratio and if external flame heating is used, the bottom of the boiler is thick enough to prevent scalding of any solid material in the wash.
Common items used as boilers include beer kegs, water heaters, and stockpots with bowls clamped on top.
In order to make the rate of boiling more constant, boiling chips are often added to the boiler.