Some time ago I installed a waste heat ejector on my system. It is teh awsome to have all that heat out of the room. Without it, recirculating waste heat raises the computer tempterature by several degrees as it keeps warming your space and being reingested.
I bought a normal ceiling box fan and a motor speed control switch (looks ike a dimmer switch). I put the fan on the floor under the desk on it's side and plenemed the opening to the back of my computer with cardboard and duct tape.
Then the output of the fan box is a 4in hose that goes to a 4 in duct pipe up through a book case and into the ceiling. It's compeltely invisible unless you realy look for it (Being surrounded by books).
Running the motor at half speed gently sucks the heat quietly away and up into the ceiling and my office is no longer a sauna on warm summer days The computer runs about 5C cooler inthe summer. In the winter I open the side of the plenem (hinged so I can get at the cabples and whatnot) and let the warm air blow under the desk like normal to help with the heating bill