4 gpu's I think you may need a heat exchanger and a hot tub for the heat you will be making. I wonder how long before people are using evaporative cooling towers to cool their crunchers at home. It is nice to have the heat in winter time, but when you need to run the a/c to keep the room cool it feels like your wasting electricity that could be running a few more crunchers. Best of luck on the GPU crunching