indirectfired

Indirect-fired refers to heating systems in which combustion occurs in a separate chamber from the material to be heated. Heat transfer to the process occurs via a heat exchanger, such as a shell-and-tube, plate, or coil arrangement, rather than by direct exposure to flame or combustion gases. This approach is contrasted with direct-fired systems, where the process fluid or product is heated directly by flames or hot gases.

In practice, indirect-fired equipment heats a primary medium—usually water or oil—in a dedicated burner section. The heated primary medium circulates through a secondary loop or exchanger that transfers heat to the process fluid or air without direct contact. Indirect-fired heaters and boilers are common in chemical processing, refineries, food and beverage production, pharmaceuticals, and district heating.

Advantages include improved control of temperature and heat quality, reduced risk of delivering fuel combustion products to the process, and greater isolation of the process from combustion equipment, which can simplify hygiene, safety, and emissions management. It also allows heating of sensitive products that might be damaged by direct flame or fuel contaminants.

Limitations include higher capital and maintenance costs, additional thermal resistance and potential heat losses in the exchanger, and slower response compared with direct-fired systems. Indirect firing is widely used when product purity, precise temperature control, or hazardous environments require separation of combustion from the process.