The function of the air inlet is to let outside air into the hot air tank and heat it by the heating device. Usually, there are heating devices such as electric heater or gas heater in the hot air water tank, and the air inlet introduces cold air into the heating device for heating, so as to raise its temperature.
The function of the air outlet is to exhaust the hot air in the hot air tank. The heated air can be used for indoor heating and drying after being exhausted through the air outlet.
To sum up, the air inlet and air outlet of the hot air box are used to introduce outside air and exhaust heated air respectively, thus realizing the functions of heating and drying.