The design principle of smoke exhaust and ventilation in kitchen is: the pipe of range hood should be as short as possible, and the length should not exceed 1.5m. The national design standard of range hood is1.5m, and the noise and exhaust data should be measured. When the flue length exceeds 1.5m, the noise exceeds the standard and the smoke exhaust capacity decreases. Only one elbow can be installed in the flue, that is, the outlet of the range hood is changed from vertical flue to horizontal flue. Adding a right-angle elbow is equivalent to lengthening the flue by 1 m. The ventilation position is as high as possible, and it is best to install it at the ceiling. The shorter the air duct, the better to reduce the damping noise of the pipeline. According to the above requirements, the range hood and exhaust fan can ensure low noise (noise is less than 55 decibels) when working; The ventilation effect reaches the design capacity.