I've got practical evidence of the downside of using a duct to draw air directly to the HSF from outside the case. HOT DAYS. I, of course, knew the conceptual logic of hotter air equals less cooling but I wasn't sure how much the effect would be. Before putting the duct in my Duron [email protected] would idle at 39c and under heavy testing would rise to 45c. After putting in the hole and duct it would idle at 33c and rise to 39c under heavy load (a temporary cardboard duct gave slightly higher temps). The room temperature was around 24c on that day of testing. This afternoon with a air temperature of 32c (and a humidity through the roof!) my machine idled at 42c and I sure wasn't gonna put it under heavy load to test it! Perhaps I should look into refridgeration for my system.