[Principle]

  The fuel is bumt at firstbox and the high temperature is produced. The quantity of heat will conduct to air to be heated through heat exchange device. Through heat exchange, the temperature of air is dropped to less than 250'C and the air will be discharged. The air to be heated is sent to hot air furnace through distribution blow fan. After absorbed heat to the rated value, the air will be sent from the vent of hot air, When the temperature of hot air reaches the rated upper limit, the burner can stop or turn to small fire autornatically When the temperature of hot air drops to the F8ted low limit, the burner can burn or turn to big fire automatically.