The length of the air ducts of exhaust fans to the outlet outside will function with air ducts up to 3 m long without significant drops in power indicators. If the length of air ducts needs to be built longer, then additional calculations are required.
As the length increases, it is necessary to increase the size (diameter) of the air ducts and at some point it may be necessary to supplement the system with other elements of the ventilation system. For complicated solutions, we invite you to contact ventilation system designers. On the other hand, in simple situations, a 3 m air duct from the exhaust fan to the outdoor outlet will not significantly reduce the ventilation capacity and will function sufficiently efficiently.