Direct fired heaters are 100 percent efficient and temperatures of upto 800°C is easily attainable. In this type of heater the fresh air is mixed with the hot flue gases.

 

The direct air heater consists of external jacket and an inner sheath to prevent radiation loss. A perforated combustion chamber made from high heat resistant steel is located centrally in the jacket. The hot gases are mixed with fresh air heated on the sides of the combustion chamber and desired hot air of homogeneous temperature is generated. Here the fuel efficiency is 100%. This is generally used for heat treatment furnaces and industrial drying applications.

 

 

 

 

Indirect fired heaters operate at an efficiency of 88-90 percent and maximum air temperature achievable is 250°C-275°C.

 

In this type of heater the fresh air is heated and delivered to process without any contamination of flue gases.