The fuel is burned through the burner to produce high-temperature gas. The heat of high temperature gas is transferred to the heated air by means of the hot blast furnace with enhanced heat exchange measures, and the temperature of high temperature gas is reduced to 250 ℃ after heat emission, and then discharged into the atmosphere. The air to be heated is forced into the hot air stove through the optional blower, and the temperature rises to the rated value after heat absorption and is sent out from the hot air outlet. When the hot air temperature reaches the upper limit of the rated temperature, the burner will automatically stop burning or automatically turn to small flame combustion. When the hot air temperature decreases to the lower limit of the rated temperature, the burner will re-ignite or turn to large fire combustion. The heating speed can be achieved by adjusting the opening of the inlet valve.