What length of hose should I use with this type of dehumidifier? 

Regarding the discharge of warm, humid air: There are two key points to understand about how these tankless desiccant dehumidifiers work. 

• If the outlet hose is likely to experience a significant temperature difference compared to the outside air, condensation will likely form inside it. You must therefore install a type of elbow that acts as a siphon to prevent water from entering the unit.
• The hose should be as short as possible to optimize performance. There is only one fan in the unit, which must handle both air intake and exhaust. If you need to extend the hose, make sure to increase its diameter immediately at the unit’s outlet to avoid overworking the fan. It is then advisable to assist the unit with a small mechanical ventilation system or an auxiliary hose motor. 

Regarding the ducting for intake and exhaust in the room:  here again, short ducts should be prioritized. The manufacturer recommends not exceeding 4 or 5 meters for both intake and exhaust. 

In summary, use the thickest possible ducts to avoid overworking the dehumidifier’s motor. This dehumidifier is not a mechanical ventilation system. 

You must increase the distances. Plan to install relief for the dehumidifier, such as small mechanical ventilation units or duct motors.