I prefer to pull outside air in (with the fan mounted opposite side of the louvered vents) across the compressor. As to not get weather elements pushing precip into the fan it is a good idea to exhaust it thru the bottom. Our "Installation" link off of our homepage shows several examples of this.This will also lower the fans sound level.A good rule of thumb in most cabinets is to use 290 cfm per dual piston compressor,single piston 140 cfm and 1/4 hp rotary vanes 140 cfm (290 better) and 3/4 hp 290 cfm and 1 hp 290 minimum (580 better)