This type of heating device is suitable for drying materials that must not be contaminated or for drying heat-sensitive materials at low temperatures. Typical applications include: milk powder, pharmaceuticals, synthetic resins, fine chemicals, etc.

In such heating systems, steam, thermal oil, flue gas, or other carriers are used to heat air through various types of heat exchangers.

The most fundamental issue with indirect hot air furnaces is heat exchange. The larger the heat exchange area, the higher the thermal conversion rate, the better the energy-saving effect of the hot air furnace, and the longer the service life of both the furnace body and heat exchanger. Conversely, the size of the heat exchange area can also be identified from the flue gas temperature—the lower the flue gas temperature, the higher the thermal conversion rate, and the larger the heat exchange area.