The heaters cause a raise in the temperature of a fluid,it can be a liquid, a gas or a mix of both, at expense of the combustion of a gas fuel in the fire tubes located at the bottom of the pressure vessel.
They are usually gas and oil flows. In such cases, the heating aims at avoiding the creation of hydrates or waxes, making future phase separations easier, or decreasing the fluid viscosity, so that its flowing through the pipes or its pumping is easier.

There are two types of heaters:
1. Direct heaters: The fire tube is surrounded by the fluid to be heated.
2. Indirect heaters: The fire tube is surrounded by the intermediate fluid, usually water, which gives energy to the fluid to be heated. This equipment can work with liquid water or with water and vapor. The coils, located at the top of the pressure vessel, carry the fluid to be heated. The heater works automatically generating the modulation and/or gas cutoff to the burners.

There are several control stages monitoring the combustion system:
1. Fluid temperature in the coil.
2. Vapor pressure within the vessel.
3. Vapor temperature within the vessel
4. Vessel water level.
5. Control system failures.

The higher or lower complexity of these systems is agreed with the customer according to their particular needs.