Abstract: A modular cooling apparatus for computer systems is disclosed. The apparatus includes an air-guiding duct, a fan coupling to the duct and a coupling apparatus for coupling the air-guiding duct and the fan to an electronics housing. The air-guiding duct has an input opening to the exterior of the electronics housing and guides ambient outside air to the input of the fan. Then the fan directs this outside air to the inside of the electronics housing. The electronic housing can be formed between a base module and the computer system circuit board or between the air-guiding duct, fan and a retention module. Furthermore, outside air is delivered in a substantially perpendicular direction relative to the plane of the computer system circuit board within the electronics housing.