| Electric resistance process heater | Electric elements transfer heat directly to a flowing process fluid or to a vessel surface. | Clean liquids and gases, small-to-medium process streams, batch vessels, and sites without a suitable fuel supply. | Precise control; no combustion products at the point of use; compact installation; high conversion of electricity into heat at the heater. | Operating cost depends on electricity prices and the power supply. High-capacity installations may require substantial electrical infrastructure. | Processes requiring accurate temperature control, a clean heat source, or straightforward installation. |
| Direct-fired process heater | Fuel combustion heats process fluid flowing through tubes exposed to hot flue gas; heat moves mainly by radiation and convection. | Refining, petrochemical, chemical, and other high-duty continuous processes. | Can provide high heat duty and high process temperatures; suited to large, continuous operations where fuel is available. | Requires combustion controls, emissions management, and careful tube-temperature and flow monitoring. Local hot spots or inadequate flow can damage tubes or process fluid. | Large, continuous-duty processes with appropriate fuel, operating expertise, and emissions controls. |
| Thermal-fluid (hot-oil) heater system | A heater warms a circulating heat-transfer fluid, which transfers heat to process equipment through a jacket, coil, or heat exchanger. | Reactors, dryers, presses, and process lines needing indirect, distributed heat. | Provides indirect heating and can serve multiple users from a circulating loop. It can deliver heat at temperatures above the boiling point of water at atmospheric pressure. | Adds pumps, piping, expansion equipment, and fluid maintenance. Heat-transfer fluid has temperature limits and may degrade if overheated. | Several process users need controlled indirect heat, especially where steam conditions are unsuitable. |
| Steam heater or heat exchanger | Steam condenses on one side of a heat-transfer surface and releases latent heat to the process fluid on the other side. | Plant-wide heating, water and liquid heating, tanks, and processes with an existing steam system. | Condensing steam transfers heat effectively and can provide relatively uniform heating. Steam is easy to distribute in facilities with established infrastructure. | Process temperature is constrained by available steam pressure and heat-exchanger approach temperature. Condensate return, water treatment, and steam-system maintenance are required. | Moderate-temperature duties at plants that already generate and distribute steam. |
| Waste-heat recovery heater | Heat from exhaust gas or another hot process stream is transferred through a heat exchanger to a process fluid or utility stream. | Facilities with hot exhaust, flue gas, or process streams that would otherwise reject useful heat. | Can reduce fuel or utility demand by recovering available heat and can improve overall plant energy efficiency. | Performance depends on the temperature, flow, and availability of the waste-heat source. Fouling, corrosion, pressure drop, and process variability must be considered. | A supplementary heat source where a dependable, compatible waste-heat stream is available. |