The fans help to reduce the tank temperature using evaporative cooling, not by blowing cold air on to the aquarium.

To achieve the best results the fan should be placed on the end of an open top aquarium so that air movement will be passed across the length and into the open room. This will allow a gentle flow of less humid air from the surrounding room over the maximum amount of water surface area. It is also possible to mount the fan on the back of the aquarium so that the air is blown forwards, this will have less of an effect but is probably the best option if the aquarium is located in a tight alcove.

If the fan is placed on a sump in an enclosed cabinet the cooling that can be achieved will be minimal or non existent. Using the fan in this way will only raise the humidity in the aquarium cabinet to a point where any extra evaporation is minimised and the cooling effect negated.