Stelter & Brinck Blog

Direct Fired Vs Indirect Fired

In a post earlier this year, we provided some industry applications of the different types of process air heaters. Today, we’ll answer what the difference is, technically, between direct fired and indirect fired?

Direct Fired Vs Indirect Fired

Direct Fired Vs Indirect Fired

“Direct Fired” means just that; the burner is fired directly into the process air stream to heat it. Air heaters that are direct fired are utilized in applications where the end product will not be affected by the by-products of combustion. Direct fired air heaters are typically less expensive and more efficient than indirect fired units, as direct-firing units converts nearly 100% of the combustion gases used to hot air. Below is a diagram of a direct fired air heater.

Direct Fired

Direct Fired

“Indirect Fired” means that the air is heated “indirectly”; the burner is fired into a heat exchanger. The air is heated when it passes over the heat exchanger and thus, the by-products of combustion remain inside the heat exchanger and do not come into direct contact with the process air. Indirect fired air heaters are used for chemically sensitive products, foods, chemicals, pharmaceuticals, ect.  Below is a diagram of an indirect fired air heater.

Indirect Fired

Indirect Fired

If you have any questions on the difference between indirect vs direct fired systems, or air heaters, contact Stelter & Brinck: 513-367-9300

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