There are two styles of hot air (preheated air) burners:
Self recuperative burners such as the immersion burner, use waste gas directly. The heat exchanger is built into the rear of the burner and the waste gas from the furnace is caused to vent from the furnace via the burner. In operation, the the heat exchanger is cooled by combustion air which is heated on its way to the burner nozzle. In some cases the pressure drop though the heat exchanger must be compensated by the use of an integral educator. Mark IV Air Cooled immersion burners are available directly from Burns Energy Systems.
Hot air burners utilizing external recuperators are usually setup to accept combustion air at maximum 450C. Preheated combustion air is generated by an external heat exchanger. In a multi-burner system, hot air from the heat exchanger is ducted to each burner using insulated pipework. As the hot air is roughly 2.5 times the volume of cold combustion air, the ductwork must have a larger cross sectional area.
The main problem with this style of recuperation is that if there are problems with the heat exchanger, whole furnace zones must be taken down for repairs. For the self recuperative style of equipment, individual burners can be serviced. In some cases the burner must be replaced, in others the heat exchanger can be repaired or replaced.