The horizontal section of the kitchen exhaust duct should not be too long. Generally, the farthest horizontal distance should not exceed 15m and there should be a slope of more than 2%. A movable joint should be set at the horizontal end to facilitate the cleaning of oil stains. The exhaust speed shall not be less than 10m/s according to regulations to prevent oil from adhering to the flue due to low wind speed. The branch pipe connected to the exhaust hood should be equipped with an air volume regulating valve.

排煙管道的設計和安裝不合理，往往會造成廚房排煙不通暢，直接影響油煙凈化器的使用。其主要原因有以下幾種：

The design and installation of smoke exhaust ducts are unreasonable, often resulting in poor ventilation of kitchen smoke, directly affecting the use of oil fume purifiers. The main reasons for this are as follows:

（1）主排煙管道通風面積不夠，氣體流速過大。根據工程經驗，排煙主管道內風速不能超過15m/s。否則在運行一個時期以后（如一年以后）很容易造成排煙系統不通暢。在油煙凈化器的運行實踐中，大部分案例都是因排煙管道通風面積不足引起的不通暢，管道內氣體的流速都在15m/s以上。

(1) The ventilation area of the main smoke exhaust duct is insufficient, and the gas flow rate is too high. According to engineering experience, the wind speed inside the smoke exhaust main duct cannot exceed 15m/s. Otherwise, after a certain period of operation (such as one year later), it is easy to cause the smoke exhaust system to be blocked. In the operation practice of oil fume purifiers, most cases are caused by insufficient ventilation area of smoke exhaust pipes, resulting in blockage. The gas flow rate in the pipes is above 15m/s.

（2）排煙管道由于要穿過建筑梁而使管道通風截面積變小，截面上阻力增加，造成氣流不通暢。

(2) Due to the need to pass through the building beam, the ventilation cross-sectional area of the smoke exhaust duct decreases, resulting in increased resistance on the cross-sectional area and obstructed airflow.

（3）排煙管道在穿過建筑梁或躲避其它設備管道時，排煙管道中的一段會低于整體排煙管道平面。在使用一段時間后，由于油水混合物會積聚在較低的那段排煙管道中，直接影響排煙通暢。

(3) When passing through building beams or avoiding other equipment pipelines, a section of the smoke exhaust pipeline will be lower than the overall plane of the smoke exhaust pipeline. After a period of use, the oil-water mixture will accumulate in the lower section of the smoke exhaust duct, directly affecting the smoothness of smoke exhaust.

（4）不同樓層的廚房油煙通過同一主管道排出，離出口近的樓層廚房排煙效果較好，而較低樓層的廚房排煙不通暢。

(4) Kitchen oil fumes from different floors are discharged through the same main pipeline. The kitchens near the exit have better smoke exhaust effect, while the kitchens on lower floors have poor smoke exhaust.

常用的排煙風機有軸流風機、風機箱和離心風機3種。

There are three commonly used smoke exhaust fans: axial flow fan, fan box, and centrifugal fan.

（1）軸流風機以前應用較多，但由于全壓小，在安裝油煙凈化器后很少應用。

(1) Axial flow fans were previously widely used, but due to their low total pressure, they were rarely used after installing oil fume purifiers.

（2）風機箱全壓中等，風量可以調節，且噪聲較低，常在集煙罩距油煙排放口距離中等的廚房排煙系統中選用。

(2) The fan box has a moderate total pressure, adjustable air volume, and low noise. It is often used in kitchen smoke exhaust systems where the distance between the hood and the oil fume discharge outlet is moderate.

（3）離心風機全壓和風量都可以調節，但由于噪聲較大，常需要做降噪處理。當廚房位于建筑物的底部時其排風機宜安放在屋頂，一方面可減少室內噪聲污染，同時排風風道處于負壓狀態，可避免氣味外溢。風機安放在屋頂時，一般選擇離心風機。

(3) The total pressure and air volume of the centrifugal fan can be adjusted, but due to the high noise, noise reduction treatment is often required. When the kitchen is located at the bottom of the building, its exhaust fan should be placed on the roof to reduce indoor noise pollution, and the exhaust duct should be in a negative pressure state to avoid odor leakage. When placing fans on the roof, centrifugal fans are generally chosen.