If you have a long duct run (3 metres or more) then this is for you
Generally, most domestic fans have axial blade impellers which are the type you will see located in most bathrooms and toilets in walls and in some ceiling installations.
However, axial blade fans have their limitations as they are really only suitable for installations up to 3 metres in a straight run, or 2 metres with a 90 degree bend. Once you get beyond this, greater consideration is required as the pressure the fan needs to move air a greater distance increases. Also,if you need to duct to an external wall which has a lot of wind and ventilating a room that gets steamy or the duct runs vertically and through a roof vent creating higher pressure, even with less than 3 metres of ducting you may wish to consider using a more powerful fan to ensure good ventilation.
In conclusion longer duct runs create more pressure. If you can imagine blowing down a half metre piece of hosepipe it’s easy. Compare this to doing the same with a 3 metre piece - obviously it will take more ‘puff’. If you then add 2 X 90 degree bends yet more ‘puff’ still is required (like when a fan is in a ceiling location – often 3 mtrs of ducting and 2 x 90 degree bends). So if you have a long duct run you need more ‘puff’ and this is when you should use a High Performance fan (known in the trade as centrifugal or mixed flow impeller fans).
High performance fans are designed to move air effectively over longer duct runs, they don’t run out of puff. They work when traditional fans don’t. Below are links to 3 of our products which give a mix of options if you need a High Performance fan.