A drum heater – also called band heater, barrel heater, container heater or canister heater- is used to reduce viscosity of liquids and gels by heating in order to fill, pump or bottle the respective liquid or to prevent liquids from freezing inside the drum. Typical liquids for the bottling application are tar

Tar

Tar is modified pitch produced primarily from the wood and roots of pine by destructive distillation under pyrolysis. Production and trade in tar was a major contributor in the economies of Northern Europe and Colonial America. Its main use was in preserving wooden vessels against rot. The largest...

, varnish

Varnish

Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss...

, resin

Resin

Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

, grease

Petroleum

Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

, chocolate

Chocolate

Chocolate is a raw or processed food produced from the seed of the tropical Theobroma cacao tree. Cacao has been cultivated for at least three millennia in Mexico, Central and South America. Its earliest documented use is around 1100 BC...

 or galantine

Galantine

A galantine is a French dish of de-boned stuffed meat, most commonly poultry or fish, that is poached and served cold, coated with aspic. Galantines are often stuffed with forcemeat, and pressed into a cylindrical shape...

.
Drum heaters are available for drums between 20 and 220 litres.

Drum Heating Ovens

Industrial Drum Ovens are designed to store and heat typically from four to twentyfour drums, usually stored in groups of four on pallets, for ease of insertion and removal by fork-lift. Heated by steam or radiant electric elements, with a single zone thermostat, they are commonly used where long term storage at a fixed temperature is required to reduce liquid viscosity or keep solids above their melt temperature. Mobile single drum electric ovens are also available.

Glass fibre mats

Drum heaters of this type have an isolated heating element

Heating element

A heating element converts electricity into heat through the process of Joule heating. Electric current through the element encounters resistance, resulting in heating of the element....

 embedded in a glass fibre mat. Silicone coated drum heaters are suitable for steel drums, whereas polyester coatings at lower temperatures can be used for plastic containers. As these heaters are flexible and wrap around the container they also called band heaters. Up to three band heaters can be applied to a standard 200 litre barrel.
There is no additional insulation so heat is lost by radiation into the surrounding air and the surface temperatures can be hot enough to burn unprotected hands.

Insulated heating jackets

These electrical drum heaters have an outer layer of insulation to protect the user and to increase energy efficiency as significantly less heat is lost to the atmosphere, and thus their power consumption is considerably less than band heaters. Typically they are designed to cover the entire surface of the drum or container.

Drum base heater

Many viscous liquids and solids stored in steel drums require considerable energy input prior to removing from the container for processing. It is sometimes beneficial to add heat directly to the underside of the drum, using a bast heater. These are available in various constructions, using induction heating, steam or silicone heater mats inside a body with sufficient mechanical strength to support the weight of a full drum.

Induction Drum Heater

Individual steel drums can be heated by mains frequency induction heating

Induction heating

Induction heating is the process of heating an electrically conducting object by electromagnetic induction, where eddy currents are generated within the metal and resistance leads to Joule heating of the metal...

. The magnetic field generated by the induction heater produces eddy currents in the drum wall, causing the steel to directly heat the contents.