An immersion heater is a fast, economical, and efficient method for heating liquids in tanks, vats, or equipment. Known as bayonet heaters, they have heating elements that can be directly inserted into a container of water, oil, or other material in order to heat the entire contents.

By using the direct heat transfer of an immersion heater, liquids quickly reach the desired temperature. Made of bundles of tubing, immersion heaters can be mounted on the side of a container or submerged in the contents. Their heating coils transfer heat to the contents, which spreads throughout the container.
Immersion heaters are a cost effective and ecologically sound method for heating material and provide a clean source of energy without leaving residual discharge or pollutants. In nuclear reactors, immersion heaters are used to keep heated water at a constant temperature for creating steam.