Heaters (or electrical heat exchangers) are made up of a group of shielded heating elements welded to a flange within a carbon-steel or stainless steel pressure casing or recipient, depending on the fluid to be heated.

This equipment is used to heat fluids (thermal oil, water, air, nitrogen, diesel, fuel-oil, other hydrocarbons, glycol,...) by passing them through the casing in the same way as a classical heat exchanger, in which the secondary fluid circuit has been substituted for the bundle of heating elements.

They are normally connected to an electrical control panel to regulate the fluid outlet temperature automatically, which forms part of the design and manufacture.

The AC regulator, normally electronic (with thyristors), maintains the desired temperature by means of its own signal or one imported from an exterior control centre (4-20 mA).

The heater and control panel are sometimes assembled together in a cabinet or structure along with a certain set of auxiliary equipment (heat exchangers, pumps, filters, valves etc.), resulting in a monoblock module (a skid), which requires more extensive engineering design.

When a heater or heating element must be installed in a potentially explosive atmosphere (in a refinery or an oil tanker, for example), explosion-proof enclosures (connection boxes) are required. At present the only Spanish manufacturer holding this specific certificate (EEx d IIC T6) is Termoelectrica Vila.