Kitchen exhaust fan vent pipe
If the fan works against the natural wind flow, a part of the kitchen exhaust air may re- enter the building.
Natural flow is from West to East on the northern Hemisphere most of the time, but could be changed by mountains, buildings, weather or geographic anomalies.
In other words, the exhaust end should be on the Lee side of the building.
Very important with kitchen exhaust fans is the interaction with furnaces, gas ovens, fire places or other combustion units in the building.
The kitchen fan could produce a relatively strong pressure decrease, which pulls the poisonous exhaust gas into the building, if the chimney effect is too weak.
That is why an interlock mechanism is mandatory in some jurisdictions.